Von Neumann universal constructor

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https://en.wikipedia.org/wiki/Von_Neumann_universal_constructor 

The first implementation of von Neumann's self-reproducing universal constructor. Three generations of machine are shown: the second has nearly finished constructing the third. The lines running to the right are the tapes of genetic instructions, which are copied along with the body of the machines. The machine shown runs in a 32-state version of von Neumann's cellular automata environment, not his original 29-state specification.

John von Neumann's universal constructor is a self-replicating machine in a cellular automaton (CA) environment. It was designed in the 1940s, without the use of a computer. The fundamental details of the machine were published in von Neumann's book Theory of Self-Reproducing Automata, completed in 1966 by Arthur W. Burks after von Neumann's death. While typically not as well known as von Neumann's other work, it is regarded as foundational for automata theory, complex systems, and artificial life. Indeed, Nobel Laureate Sydney Brenner considered Von Neumann's work on self-reproducing automata (together with Turing's work on computing machines) central to biological theory as well, allowing us to "discipline our thoughts about machines, both natural and artificial."

Von Neumann's goal, as specified in his lectures at the University of Illinois in 1949, was to design a machine whose complexity could grow automatically akin to biological organisms under natural selection. He asked what is the threshold of complexity that must be crossed for machines to be able to evolve. His answer was to specify an abstract machine which, when run, would replicate itself. In his design, the self-replicating machine consists of three parts: a "description" of ('blueprint' or program for) itself, a universal constructor mechanism that can read any description and construct the machine (sans description) encoded in that description, and a universal copy machine that can make copies of any description. After the universal constructor has been used to construct a new machine encoded in the description, the copy machine is used to create a copy of that description, and this copy is passed on to the new machine, resulting in a working replication of the original machine that can keep on reproducing. Some machines will do this backwards, copying the description and then building a machine. Crucially, the self-reproducing machine can evolve by accumulating mutations of the description, not the machine itself, thus gaining the ability to grow in complexity.

To define his machine in more detail, von Neumann invented the concept of a cellular automaton. The one he used consists of a two-dimensional grid of cells, each of which can be in one of 29 states at any point in time. At each timestep, each cell updates its state depending on the states of the surrounding cells at the prior timestep. The rules governing these updates are identical for all cells.

The universal constructor is a certain pattern of cell states in this cellular automaton. It contains one line of cells that serve as the description (akin to Turing's tape), encoding a sequence of instructions that serve as a 'blueprint' for the machine. The machine reads these instructions one by one and performs the corresponding actions. The instructions direct the machine to use its 'construction arm' (another automaton that functions like an Operating System) to build a copy of the machine, without the description tape, at some other location in the cell grid. The description cannot contain instructions to build an equally long description tape, just as a container cannot contain a container of the same size. Therefore, the machine includes the separate copy machine which reads the description tape and passes a copy to the newly constructed machine. The resulting new set of universal constructor and copy machines plus description tape is identical to the old one, and it proceeds to replicate again.

Purpose

Von Neumann's System of Self-Replication Automata with the ability to evolve (Figure adapted from Luis Rocha's Lecture Notes at Binghamton University). i) the self-replicating system is composed of several automata plus a separate description (an encoding formalized as a Turing 'tape') of all the automata: Universal Constructor (A), Universal Copier (B), Operating System (C), extra functions not involved with replication (D), and separate description Φ(A,B,C,D) encoding all automata. ii) (Top) Universal Constructor produces (decodes) automata from their description (active mode of description); (Bottom) Universal Copier copies description of automata (passive mode of description); Mutations Φ(D') to description Φ(D) (not changes in automaton D directly) propagate to the set of automata produced in next generation, allowing (automata + description) system to continue replicating and evolving (D → D'). The active process of construction from a description parallels DNA translation, the passive process of copying the description parallels DNA replication, and inheritance of mutated descriptions parallels Vertical inheritance of DNA mutations in Biology, and were proposed by Von Neumann before the discovery of the structure of the DNA molecule and how it is separately translated and replicated in the Cell.

Von Neumann's design has traditionally been understood to be a demonstration of the logical requirements for machine self-replication. However, it is clear that far simpler machines can achieve self-replication. Examples include trivial crystal-like growth, template replication, and Langton's loops. But von Neumann was interested in something more profound: construction, universality, and evolution.

Note that the simpler self-replicating CA structures (especially, Byl's loop and the Chou–Reggia loop) cannot exist in a wide variety of forms and thus have very limited evolvability. Other CA structures such as the Evoloop are somewhat evolvable but still don't support open-ended evolution. Commonly, simple replicators do not fully contain the machinery of construction, there being a degree to which the replicator is information copied by its surrounding environment. Although the Von Neumann design is a logical construction, it is in principle a design that could be instantiated as a physical machine. Indeed, this universal constructor can be seen as an abstract simulation of a physical universal assembler. The issue of the environmental contribution to replication is somewhat open, since there are different conceptions of raw material and its availability.

Von Neumann's crucial insight is that the description of the machine, which is copied and passed to offspring separately via the universal copier, has a double use; being both an active component of the construction mechanism in reproduction, and being the target of a passive copying process. This part is played by the description (akin to Turing's tape of instructions) in Von Neumann's combination of universal constructor and universal copier. The combination of a universal constructor and copier, plus a tape of instructions conceptualizes and formalizes i) self-replication, and ii) open-ended evolution, or growth of complexity observed in biological organisms.

This insight is all the more remarkable because it preceded the discovery of the structure of the DNA molecule by Watson and Crick and how it is separately translated and replicated in the cell—though it followed the Avery–MacLeod–McCarty experiment which identified DNA as the molecular carrier of genetic information in living organisms. The DNA molecule is processed by separate mechanisms that carry out its instructions (translation) and copy (replicate) the DNA for newly constructed cells. The ability to achieve open-ended evolution lies in the fact that, just as in nature, errors (mutations) in the copying of the genetic tape can lead to viable variants of the automaton, which can then evolve via natural selection. As Brenner put it:

Turing invented the stored-program computer, and von Neumann showed that the description is separate from the universal constructor. This is not trivial. Physicist Erwin Schrödinger confused the program and the constructor in his 1944 book What is Life?, in which he saw chromosomes as ″architect's plan and builder's craft in one″. This is wrong. The code script contains only a description of the executive function, not the function itself.

— Sydney Brenner

Evolution of Complexity

Von Neumann's goal, as specified in his lectures at the University of Illinois in 1949, was to design a machine whose complexity could grow automatically akin to biological organisms under natural selection. He asked what is the threshold of complexity that must be crossed for machines to be able to evolve and grow in complexity. His “proof-of-principle” designs showed how it is logically possible. By using an architecture that separates a general purpose programmable (“universal”) constructor from a general purpose copier, he showed how the descriptions (tapes) of machines could accumulate mutations in self-replication and thus evolve more complex machines (the image below illustrates this possibility.). This is a very important result, as prior to that, it might have been conjectured that there is a fundamental logical barrier to the existence of such machines; in which case, biological organisms, which do evolve and grow in complexity, could not be “machines”, as conventionally understood. Von Neumann's insight was to think of life as a Turing Machine, which, is similarly defined by a state-determined machine "head" separated from a memory tape.

In practice, when we consider the particular automata implementation Von Neumann pursued, we conclude that it does not yield much evolutionary dynamics because the machines are too fragile - the vast majority of perturbations cause them effectively to disintegrate. Thus, it is the conceptual model outlined in his Illinois lectures that is of greater interest today because it shows how a machine can in principle evolve. This insight is all the more remarkable because the model preceded the discovery of the structure of the DNA molecule as discussed above. It is also noteworthy that Von Neumann's design considers that mutations towards greater complexity need to occur in the (descriptions of) subsystems not involved in self-reproduction itself, as conceptualized by the additional automaton D he considered to perform all functions not directly involved in reproduction (see Figure above with Von Neumann's System of Self-Replication Automata with the ability to evolve.) Indeed, in biological organisms only very minor variations of the genetic code have been observed, which matches Von Neumann's rationale that the universal constructor (A) and Copier (B) would not themselves evolve, leaving all evolution (and growth of complexity) to automaton D. In his unfinished work, Von Neumann also briefly considers conflict and interactions between his self-reproducing machines, towards understanding the evolution of ecological and social interactions from his theory of self-reproducing machines.

A demonstration of the ability of von Neumann's machine to support inheritable mutations. (1) At an earlier timestep, a mutation was manually added to the second generation machine's tape. (2) Later generations both display the phenotype of the mutation (a drawing of a flower) and pass the mutation on to their children, since the tape is copied each time. This example illustrates how von Neumann's design allows for complexity growth (in theory) since the tape could specify a machine that is more complex than the one making it.

Implementations

In automata theory, the concept of a universal constructor is non-trivial because of the existence of Garden of Eden patterns. But a simple definition is that a universal constructor is able to construct any finite pattern of non-excited (quiescent) cells.

Arthur Burks and others extended the work of von Neumann, giving a much clearer and complete set of details regarding the design and operation of von Neumann's self-replicator. The work of J. W. Thatcher is particularly noteworthy, for he greatly simplified the design. Still, their work did not yield a complete design, cell by cell, of a configuration capable of demonstrating self-replication.

Renato Nobili and Umberto Pesavento published the first fully implemented self-reproducing cellular automaton in 1995, nearly fifty years after von Neumann's work. They used a 32-state cellular automaton instead of von Neumann's original 29-state specification, extending it to allow for easier signal-crossing, explicit memory function and a more compact design. They also published an implementation of a general constructor within the original 29-state CA but not one capable of complete replication - the configuration cannot duplicate its tape, nor can it trigger its offspring; the configuration can only construct.

In 2004, D. Mange et al. reported an implementation of a self-replicator that is consistent with the designs of von Neumann.

In 2007, Nobili published a 32-state implementation that uses run-length encoding to greatly reduce the size of the tape.

In 2008, William R. Buckley published two configurations which are self-replicators within the original 29-state CA of von Neumann. Buckley claims that the crossing of signal within von Neumann 29-state cellular automata is not necessary to the construction of self-replicators. Buckley also points out that for the purposes of evolution, each replicator should return to its original configuration after replicating, in order to be capable (in theory) of making more than one copy. As published, the 1995 design of Nobili-Pesavento does not fulfill this requirement but the 2007 design of Nobili does; the same is true of Buckley's configurations.

In 2009, Buckley published with Golly a third configuration for von Neumann 29-state cellular automata, which can perform either holistic self-replication, or self-replication by partial construction. This configuration also demonstrates that signal crossing is not necessary to the construction of self-replicators within von Neumann 29-state cellular automata.

C. L. Nehaniv in 2002, and also Y. Takada et al. in 2004, proposed a universal constructor directly implemented upon an asynchronous cellular automaton, rather than upon a synchronous cellular automaton. 

Comparison of implementations

Implementation	Source	Ruleset	Rectangular area	Number of cells	Length of tape	Ratio	Period	Tape code compression	Tape code length	Tape code type	Replication mechanism	Replication type	Growth rate
Nobili-Pesavento, 1995		Nobili 32-state	97 × 170	6,329	145,315	22.96	6.34 × 1010	none	5 bits	binary	holistic constructor	non-repeatable	linear
Nobili, 2007	SR_CCN_AP.EVN	Nobili 32-state	97 × 100	5,313	56,325	10.60	9.59 × 109	run-length limited encoding	5 bits	binary	holistic constructor	repeatable	super-linear
Buckley, 2008	codon5.rle	Nobili 32-state	112 × 50	3,343	44,155	13.21	5.87 × 109	auto-retraction	5 bits	binary	holistic constructor	repeatable	linear
Buckley, 2008	replicator.mc	von Neumann 29-state	312 × 132	18,589	294,844	15.86	2.61 × 1011	auto-retraction	5 bits	binary	holistic constructor	repeatable	linear
Buckley, 2008	codon4.rle	Nobili 32-state	109 × 59	3,574	37,780	10.57	4.31 × 109	auto-retraction/bit generation	4 bits	binary	holistic constructor	repeatable	linear
Buckley, 2009	codon3.rle	Nobili 32-state	116 × 95	4,855	23,577	4.86	1.63 × 109	auto-retraction/bit generation/code overlay	3 bits	binary	holistic constructor	repeatable	super-linear
Buckley, 2009	PartialReplicator.mc	von Neumann 29-state	2063 × 377	264,321	N/A	—	≈1.12 × 1014	none	4 bits	binary	partial constructor	repeatable	linear
Goucher & Buckley, 2012	phi9.rle	Nobili 32-state	122 × 60	3957	8920	2.25	—	auto-retraction/bit generation/code overlay/run length limited	3+ bits	ternary	holistic constructor	repeatable	super-linear

As defined by von Neumann, universal construction entails the construction of passive configurations, only. As such, the concept of universal construction constituted nothing more than a literary (or, in this case, mathematical) device. It facilitated other proof, such as that a machine well constructed may engage in self-replication, while universal construction itself was simply assumed over a most minimal case. Universal construction under this standard is trivial. Hence, while all the configurations given here can construct any passive configuration, none can construct the real-time crossing organ devised by Gorman.

Practicality and computational cost

All the implementations of von Neumann's self-reproducing machine require considerable resources to run on computer. For example, in the Nobili-Pesavento 32-state implementation shown above, while the body of the machine is just 6,329 non-empty cells (within a rectangle of size 97x170), it requires a tape that is 145,315 cells long, and takes 63 billion timesteps to replicate. A simulator running at 1,000 timesteps per second would take over 2 years to make the first copy. In 1995, when the first implementation was published, the authors had not seen their own machine replicate. However, in 2008, the hashlife algorithm was extended to support the 29-state and 32-state rulesets in Golly. On a modern desktop PC, replication now takes only a few minutes, although a significant amount of memory is required.

Animation gallery

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  Example of a 29-state read arm.

Kidnapping

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Kidnapping 

El Malón, by Johann Moritz Rugendas (1802–1858), historic painting depicting kidnapping of a woman.

 

Part of a series on
Kidnapping
Types
Child abduction Groom and Bride kidnapping Express kidnapping Tiger kidnapping Fake kidnapping Political kidnapping Shanghaiing Impressment Extraordinary rendition Forced disappearance Ransom
By country
Canada China South Africa United Kingdom United States

In criminal law, kidnapping is the unlawful confinement of a person against their will, often including transportation/asportation. The asportation and abduction element is typically but not necessarily conducted by means of force or fear: the perpetrator may use a weapon to force the victim into a vehicle, but it is still kidnapping if the victim is enticed to enter the vehicle willingly (e.g. in the belief that it is a taxicab).

K. J. Ståhlberg (in the center-right), the first President of the Republic of Finland, and his wife at the Helsinki Central Station after their kidnapping. In the middle of picture their daughter Elli Ståhlberg stands behind them.

Kidnapping may be done to demand for ransom in exchange for releasing the victim, or for other illegal purposes.  Kidnapping can be accompanied by bodily injury which elevates the crime to aggravated kidnapping.

Kidnapping of a child is known as child abduction, which is sometimes a separate legal category.

Motivations

The abduction of Dinah, (watercolor circa 1896–1902 by James Tissot)

Kidnapping of children is usually done by one parent or others. The kidnapping of adults is often for ransom or to force someone to withdraw money from an ATM, but may also be for sexual assault. Children have also been kidnapped for the commission of sexual assault.

In the past, and presently in some parts of the world (such as southern Sudan), kidnapping is a common means used to obtain slaves and money through ransom. In less recent times, kidnapping in the form of shanghaiing (or "pressganging") men were used to supply merchant ships in the 19th century with sailors, whom the law considered unfree labour.

Criminal gangs are estimated to make up to $500 million a year in ransom payments from kidnapping.

Kidnapping has been identified as one source by which terrorist organizations have been known to obtain funding. The Perri, Lichtenwald and MacKenzie article identified "tiger" kidnapping as a specific method used by either the Real Irish Republican Army or Continuity Irish Republican Army, in which a kidnapped family member is used to force someone to steal from their employer.

• Bride kidnapping is a term often applied loosely, to include any bride "abducted" against the will of her parents, even if she is willing to marry the "abductor". It still is traditional amongst certain nomadic peoples of Central Asia. It has seen a resurgence in Kyrgyzstan since the fall of the Soviet Union and the subsequent erosion of women's rights.
• Express kidnapping is a method of abduction used in some countries, mainly from Latin America, where a small ransom, that a company or family can easily pay, is demanded.
• Tiger kidnapping is taking a hostage to make a loved one or associate of the victim do something (e.g. a child is taken hostage to force the shopkeeper to open the safe). The term originates from the usually long preceding observation, like a tiger does on the prowl.

Kidnapping has sometimes been used by the family and friends of a member of an alleged cult as a method to remove the member from the alleged cult and begin a deprogramming process. Deprogramming and exit counseling have been used with the purpose of getting alleged cult members to abandon their groups' beliefs. The danger presented by cult groups has been used by deprogrammers to justify using the extreme act of kidnapping to get alleged members to change their allegiance away from the group.

By jurisdiction

Australia

In Australia, kidnapping is a criminal offence, as defined by either the State crimes act, or the Commonwealth Criminal Code. It is a serious indictable offence, and is punishable by up to 14 – 25 years imprisonment.

Canada

Kidnapping that does not result in a homicide is a hybrid offence that comes with a maximum possible penalty of life imprisonment (18 months if tried summarily). A murder that results from kidnapping is classified as 1st-degree, with a sentence of life imprisonment that results from conviction (the mandatory penalty for murder under Canadian law).

Colombia

According to a 2022 study by political scientost Danielle Gilbert, armed groups in Colombia engage in ransom kidnappings as a way to maintain the armed groups' local systems of taxation. The groups resort to ransom kidnappings to punish tax evasion and incentivize inhabitants not to shirk.

Netherlands

Article 282 prohibits hostaging (and 'kidnapping' is a kind of 'hostaging'). Part 1 of Article 282 allows sentencing kidnappers to maximum imprisonment of 8 years or a fine of the fifth category. Part 2 allows maximum imprisonment of 9 years or a fine of the fifth category if there are serious injuries. Part 3 allows maximum imprisonment of 12 years or a fine of the fifth category if the victim has been killed. Part 4 allows sentencing people that collaborate with kidnapping (such as proposing or make available a location where the victim hostaged). Part 1, 2 and 3 will apply also to them.

United Kingdom

Kidnapping is an offence under the common law of England and Wales. Lord Brandon said in 1984 R v D:

First, the nature of the offence is an attack on, and infringement of, the personal liberty of an individual. Secondly, the offence contains four ingredients as follows: (1) the taking or carrying away of one person by another; (2) by force or fraud; (3) without the consent of the person so taken or carried away; and (4) without lawful excuse.

In all cases of kidnapping of children, where it is alleged that a child has been kidnapped, it is the absence of the consent of that child which is material. This is the case regardless of the age of the child. A very small child will not have the understanding or intelligence to consent. This means that absence of consent will be a necessary inference from the age of the child. It is a question of fact for the jury whether an older child has sufficient understanding and intelligence to consent. Lord Brandon said: "I should not expect a jury to find at all frequently that a child under fourteen had sufficient understanding and intelligence to give its consent." If the child (being capable of doing so) did consent to being taken or carried away, the fact that the person having custody or care and control of that child did not consent to that child being taken or carried away is immaterial. If, on the other hand, the child did not consent, the consent of the person having custody or care and control of the child may support a defence of lawful excuse. It is known as Gillick competence.

Regarding restriction on prosecution, no prosecution may be instituted, except by or with the consent of the Director of Public Prosecutions, for an offence of kidnapping if it was committed against a child under the age of sixteen and by a person connected with the child, within the meaning of section 1 of the Child Abduction Act 1984. Kidnapping is an indictable-only offence. Kidnapping is punishable with imprisonment or fine at the discretion of the court. There is no limit on the fine or the term of imprisonment that may be imposed provided the sentence is not inordinate.

A parent should only be prosecuted for kidnapping their own child "in exceptional cases, where the conduct of the parent concerned is so bad that an ordinary right-thinking person would immediately and without hesitation regard it as criminal in nature".

United States

Main article: Kidnapping in the United States

Law in the United States follows from English common law. Following the highly publicized 1932 Lindbergh kidnapping, Congress passed the Federal Kidnapping Act, which authorized the FBI to investigate kidnapping at a time when the Bureau was expanding in size and authority. The fact that a kidnapped victim may have been taken across state lines brings the crime within the ambit of federal criminal law.

Most states recognize different types of kidnapping and punish according to such factors as the location, duration, method, manner and purpose of the offense. There are several deterrents to kidnapping in the United States of America. Among these are:

1. The extreme logistical challenges involved in successfully exchanging the money for the return of the victim without being apprehended or surveiled.
2. Harsh punishment. Convicted kidnappers face lengthy prison terms. If a victim is brought across state lines, federal charges can be laid as well.
3. Good cooperation and information sharing between law enforcement agencies, and tools for spreading information to the public (such as the AMBER Alert system).

One notorious failed example of kidnap for ransom was the 1976 Chowchilla bus kidnapping, in which 26 children were abducted with the intention of bringing in a $5 million ransom. The children and driver escaped from an underground van without the aid of law enforcement. According to the Department of Justice, kidnapping makes up 2% of all reported violent crimes against juveniles.

From the 1990s on, the New York divorce coercion gang was involved in the kidnapping and torture of Jewish husbands in New York City and New Jersey for the purpose of forcing them to grant gittin (religious divorces) to their wives. They were finally apprehended on October 9, 2013, in connection with a foiled kidnapping plot.

According to a 2003 Domestic Violence Report in Colorado, out of a survey of 189 incidents, most people (usually white females) are taken from their homes or residence by a present or former spouse or significant other. They are usually taken by force, not by weapon, and usually the victims are not injured when they are freed.

In 2009, Phoenix, Arizona reported over 300 cases of kidnapping, although subsequent investigation found that the Phoenix police falsified data. "Phoenix Kidnappings: Uncovering the Truth". Archived from the original on 2013-04-13. If true, this would have been the highest rate of any U.S. city and second in the world only to Mexico City. A rise in kidnappings in the southwestern United States in general has been attributed to misclassification by local police, lack of a unified standard, desire for Federal grants, or the Mexican Drug War.

In 2010, the United States was ranked sixth in the world (by absolute numbers, not per capita) for kidnapping for ransom, according to the available statistics (after Colombia, Italy, Lebanon, Peru, and the Philippines).

In 2009, the Los Angeles Times named Phoenix, Arizona, as America's kidnapping capital, reporting that every year hundreds of ransom kidnappings occur there, virtually all within the underworld associated with human and drug smuggling from Mexico, and often done as a way of collecting unpaid debts. However, a later audit by the U.S. Department of Justice Inspector General found only 59 federally reportable kidnappings in 2008, compared to the over 300 claimed on grant applications.

During the year 1999 in the United States, 203,900 children were reported as the victims of family abductions and 58,200 of non-family abductions. However, only 115 were the result of "stereotypical" kidnaps (by someone unknown or of slight acquaintance to the child, held permanently or for ransom).

Statistics

Global kidnapping hotspots

	1999	2006	2014
1	Colombia	Mexico	Mexico
2	Mexico	Iraq	India
3	Brazil	India	Pakistan
4	Philippines	South Africa	Iraq
5	Venezuela	Brazil	Nigeria
6	Ecuador	Pakistan	Libya
7	Russia and CIS	Ecuador	Afghanistan
8	Nigeria	Venezuela	Bangladesh
9	India	Colombia	Sudan
10	South Africa	Bangladesh	Lebanon

Countries with the highest rates

Arrested kidnappers in Rio de Janeiro, Brazil lying on the ground

Kidnapping for ransom is a common occurrence in various parts of the world today, and certain cities and countries are often described as the "Kidnapping Capital of the World". In 2018 the UN found Pakistan and England had the highest amount of kidnappings while New Zealand had the highest rate among the 70 countries for which data is available. As of 2007, that title belonged to Iraq with possibly 1,500 foreigners kidnapped. In 2004, it was Mexico, and in 2001, it was Colombia. Statistics are harder to come by. Reports suggest a world total of 12,500–25,500 per year with 3,600 per year in Colombia and 3,000 per year in Mexico around the year 2000. However, by 2016, the number of kidnappings in Colombia had declined to 205 and it continues to decline. Mexican numbers are hard to confirm because of fears of police involvement in kidnapping. "Kidnapping seems to flourish particularly in fragile states and conflict countries, as politically motivated militias, organized crime and the drugs mafia fill the vacuum left by government".

Pirates

Kidnapping on the high seas in connection with piracy has been increasing. It was reported that 661 crewmembers were taken hostage and 12 kidnapped in the first nine months of 2009. The IMB Piracy Reporting Centre recorded that 141 crew members were taken hostage and 83 were kidnapped in 2018.

Angkor Wat

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Angkor_Wat 

 

Angkor Wat

Front side of the main complex
Location	Siem Reap, Cambodia
Coordinates	13°24′45″N 103°52′0″ECoordinates: 13°24′45″N 103°52′0″E
Altitude	65 m (213 ft)
History
Builder	Started by Suryavarman II Completed by Jayavarman VII
Founded	12th century
Cultures	Khmer Empire
Architecture
Architectural styles	Khmer (Angkor Wat style)
UNESCO World Heritage Site
Official name	Angkor
Type	Cultural
Criteria	i, ii, iii, iv
Designated	1992 (16th session)
Reference no.	668
Region	Asia and the Pacific

Angkor Wat (/ˌæŋkɔːr ˈwɒt/; Khmer: អង្គរវត្ត, "City/Capital of Temples") is a temple complex in Cambodia and is the largest religious monument in the world, on a site measuring 162.6 hectares (1,626,000 m²; 402 acres). Originally constructed as a Hindu temple dedicated to the god Vishnu for the Khmer Empire, it was gradually transformed into a Buddhist temple towards the end of the 12th century as such it is also described as a "Hindu-Buddhist" temple.

It was built by the Khmer King Suryavarman II in the early 12th century in Yaśodharapura (Khmer: យសោធរបុរៈ, present-day Angkor), the capital of the Khmer Empire, as his state temple and eventual mausoleum. Breaking from the Shaiva tradition of previous kings, Angkor Wat was instead dedicated to Vishnu. As the best-preserved temple at the site, it is the only one to have remained a significant religious centre since its foundation. The temple is at the top of the high classical style of Khmer architecture. It has become a symbol of Cambodia, appearing on its national flag, and it is the country's prime attraction for visitors.

Angkor Wat combines two basic plans of Khmer temple architecture: the temple-mountain and the later galleried temple. It is designed to represent Mount Meru, home of the devas in Hindu mythology: within a moat more than 5 kilometres (3 mi) long and an outer wall 3.6 kilometres (2.2 mi) long are three rectangular galleries, each raised above the next. At the centre of the temple stands a quincunx of towers. Unlike most Angkorian temples, Angkor Wat is oriented to the west; scholars are divided as to the significance of this. The temple is admired for the grandeur and harmony of the architecture, its extensive bas-reliefs, and for the numerous devatas adorning its walls.

As the best-preserved temple at the site, Angkor Wat is the only one to have remained a significant religious centre since its foundation. The temple is at the top of the high classical style of Khmer architecture. It is one of the most important pilgrimage sites for Buddhists in Cambodia and around the world, having played a major role in converting Cambodia into a Buddhist nation. It has become a symbol of Cambodia, appearing on its national flag, and is the country's main tourist attraction.

Etymology

The modern name Angkor Wat, alternatively Nokor Wat, means "Temple City" or "City of Temples" in Khmer. Angkor (អង្គរ ângkôr) meaning "city" or "capital city", is a vernacular form of the word nokor (នគរ nôkôr), which comes from the Sanskrit/Pali word nagara (Devanāgarī: नगर). Wat (វត្ត vôtt) is the word for "temple grounds", also derived from Sanskrit/Pali vāṭa (Devanāgarī: वाट), meaning "enclosure".

The original name of the temple was Vrah Viṣṇuloka or Parama Viṣṇuloka meaning "the sacred dwelling of Vishnu."

History

King Suryavarman II, the builder of Angkor Wat

Angkor Wat lies 5.5 kilometres (3+1⁄2 mi) north of the modern town of Siem Reap, and a short distance south and slightly east of the previous capital, which was centred at Baphuon. In an area of Cambodia where there is an essential group of ancient structures, it is the southernmost of Angkor's main sites.

According to a myth, the construction of Angkor Wat was ordered by Indra to serve as a palace for his son Precha Ket Mealea. According to the 13th-century Chinese traveller Zhou Daguan, some believed that the temple was constructed in a single night by a divine architect.

The brahmin by the name of Divākarapaṇḍita was responsible for urging King Suryavarman II to construct Angkor Wat. The initial design and construction of the temple took place in the first half of the 12th century, during the reign of Suryavarman II (ruled 1113 – c. 1150). All of the original religious motifs derived from Hinduism. Breaking from the Shaiva tradition of previous kings, Angkor Wat was instead dedicated to Vishnu. It was built as the king's state temple and capital city. As neither the foundation stela nor any contemporary inscriptions referring to the temple have been found, its original name is unknown, but it may have been known as "Varah Vishnu-lok" after the presiding deity. Work seems to have ended shortly after the king's death, leaving some of the bas-relief decoration unfinished. The term Vrah Viṣṇuloka or Parama Viṣṇuloka literally means "The king who has gone to the supreme world of Vishnu", which refer to Suryavarman II posthumously and intend to venerate his glory and memory.

In 1177, approximately 27 years after the death of Suryavarman II, Angkor was sacked by the Chams, the traditional enemies of the Khmer. Thereafter the empire was restored by a new king, Jayavarman VII, who established a new capital and state temple (Angkor Thom and the Bayon, respectively), a few kilometers north, dedicated to Buddhism, because the king believed that the Hindu gods had failed him. Angkor Wat was therefore also gradually converted into a Buddhist site, and many Hindu sculptures were replaced by Buddhist art.

Facade of Angkor Wat, a drawing by Henri Mouhot, c. 1860

 

Sketch of Angkor Wat, a drawing by Louis Delaporte, c. 1880

 

Early photograph of Angkor Wat in 1866, taken by Emile Gsell

Towards the end of the 12th century, Angkor Wat gradually transformed from a Hindu centre of worship to Buddhism, which continues to the present day. Angkor Wat is unusual among the Angkor temples in that although it was largely neglected after the 16th century, it was never completely abandoned. Fourteen inscriptions dated from the 17th century, discovered in the Angkor area, testify to Japanese Buddhist pilgrims that had established small settlements alongside Khmer locals. At that time, the temple was thought by the Japanese visitors to be the famed Jetavana garden of the Buddha, which was originally located in the kingdom of Magadha, India. The best-known inscription tells of Ukondayu Kazufusa, who celebrated the Khmer New Year at Angkor Wat in 1632.

Buddhist monks in front of the reflection pool at Angkor Wat, Cambodia

One of the first Western visitors to the temple was António da Madalena, a Portuguese friar who visited in 1586 and said that it "is of such extraordinary construction that it is not possible to describe it with a pen, particularly since it is like no other building in the world. It has towers and decoration and all the refinements which the human genius can conceive of."

In 1622, The Poem of Angkor Wat composed in Khmer verse describes the beauty of Angkor Wat and creates a legend around the construction of the complex, supposedly a divine castle built for legendary Khmer king Preah Ket Mealea by Hindu god Preah Pisnukar (or Braḥ Bisṇukār, Vishvakarman), as Suryavarman II had already vanished from people's minds.

In 1860, with the help of French missionary Father Charles-Émile Bouillevaux, the temple was effectively rediscovered by the French naturalist and explorer Henri Mouhot, who popularised the site in the West through the publication of travel notes, in which he wrote:

One of these temples, a rival to that of Solomon, and erected by some ancient Michelangelo, might take an honorable place beside our most beautiful buildings. It is grander than anything left to us by Greece or Rome, and presents a sad contrast to the state of barbarism in which the nation is now plunged.

In 1861 German anthropologist Aldof Bastian undertook a four-year trip to Southeast Asia and his account of this trip, The People of East Asia ran to six volumes. when Bastian finally published the studies and observations during his Journey through Cambodia to Cochinchina in Germany in 1868 - told in detail but uninspiredly, above all without a single one of his drawings of the Angkorian sites - this work hardly made an impression, while everyone was talking about Henri Mouhot's posthumous work with vivid descriptions of Angkor, Travels in the Central Parts of Indo-China, Siam, Cambodia and Laos, published in 1864 through the Royal Geographical Society.

There were no ordinary dwellings or houses or other signs of settlement, including cooking utensils, weapons, or items of clothing usually found at ancient sites. Instead, there is only evidence of the monuments themselves.

The grand replica of Angkor Wat at the Paris Colonial Exposition (1931) represented the immense grandeur of the French protectorate of Cambodia.

The artistic legacy of Angkor Wat and other Khmer monuments in the Angkor region led directly to France adopting Cambodia as a protectorate on 11 August 1863 and invading Siam to take control of the ruins. This quickly led to Cambodia reclaiming lands in the northwestern corner of the country such as the areas of Siem Reap, Battambang and Sisophon which were under Siamese rule from 1795 to 1907.

Angkor Wat's aesthetics were on display in the plaster cast museum of Louis Delaporte called musée Indo-chinois which existed in the Parisian Trocadero Palace from c.1880 to the mid-1920s.

The 20th century saw a considerable restoration of Angkor Wat. Gradually teams of laborers and archeologists pushed back the jungle and exposed the expanses of stone, permitting the sun to once again illuminate the dark corners of the temple. Angkor Wat caught the attention and imagination of a wider audience in Europe when the pavilion of French protectorate of Cambodia, as part of French Indochina, recreated the life-size replica of Angkor Wat during Paris Colonial Exposition in 1931.

Cambodia gained independence from France on 9 November 1953 and has controlled Angkor Wat since that time. It is safe to say that from the colonial period onwards until the site's nomination as UNESCO World Heritage in 1992, this specific temple of Angkor Wat was instrumental in the formation of the modern and gradually globalised concept of built cultural heritage.

Bullet holes left by a shoot-out between the Khmer Rouge and Vietnamese forces at Angkor Wat

Restoration work was interrupted by the Cambodian Civil War and Khmer Rouge control of the country during the 1970s and 1980s, but relatively little damage was done during this period. Camping Khmer Rouge forces used whatever wood remained in the building structures for firewood, and a shoot-out between Khmer Rouge and Vietnamese forces put a few bullet holes in a bas relief. Far more damage was done after the wars, by art thieves working out of Thailand, which, in the late 1980s and early 1990s, claimed almost every head that could be lopped off the structures, including reconstructions.

The temple is a powerful symbol of Cambodia, and is a source of great national pride that has factored into Cambodia's diplomatic relations with France, the United States, and its neighbour Thailand. A depiction of Angkor Wat has been a part of Cambodian national flags since the introduction of the first version circa 1863. From a larger historical and even transcultural perspective, however, the temple of Angkor Wat did not become a symbol of national pride sui generis but had been inscribed into a larger politico-cultural process of French-colonial heritage production in which the original temple site was presented in French colonial and universal exhibitions in Paris and Marseille between 1889 and 1937.

In December 2015, it was announced that a research team from University of Sydney had found a previously unseen ensemble of buried towers built and demolished during the construction of Angkor Wat, as well as a massive structure of unknown purpose on its south side and wooden fortifications. The findings also include evidence of low-density residential occupation in the region, with a road grid, ponds, and mounds. These indicate that the temple precinct, bounded by moat and wall, may not have been used exclusively by the priestly elite, as was previously thought. The team used LiDAR, ground-penetrating radar and targeted excavation to map Angkor Wat.

Architecture

Site and plan

Main article: Angkor Wat Equinox

 

Plan of Angkor Wat

 

The general layout of Angkor Wat with its central structure in the middle

 

An aerial view of Angkor Wat

Angkor Wat is a unique combination of the temple mountain (the standard design for the empire's state temples) and the later plan of concentric galleries, most of which were derived from religious beliefs of Hinduism originally. The construction of Angkor Wat also suggests that there was a celestial significance with certain features of the temple. This is observed in the temple's east–west orientation, and lines of sight from terraces within the temple that show specific towers to be at the precise location of the sunrise on a solstice. The temple is a representation of Mount Meru, the home of the gods according to Hindu mythology: the central quincunx of towers symbolises the five peaks of the mountain, and the walls and moat symbolize the surrounding mountain ranges and ocean. Access to the upper areas of the temple was progressively more exclusive, with the laity being admitted only to the lowest level.

A detailed plan of the central structure

The Angkor Wat temple's main tower aligns to the morning sun of the spring equinox. Unlike most Khmer temples, Angkor Wat is oriented to the west rather than the east. This has led many (including Maurice Glaize and George Coedès) to conclude that Suryavarman intended it to serve as his funerary temple. Further evidence for this view is provided by the bas-reliefs, which proceed in a counter-clockwise direction—prasavya in Hindu terminology—as this is the reverse of the normal order. Rituals take place in reverse order during Brahminic funeral services.

Archaeologist Charles Higham also describes a container which may have been a funerary jar which was recovered from the central tower. It has been nominated by some as the greatest expenditure of energy on the disposal of a corpse. Freeman and Jacques, however, note that several other temples of Angkor depart from the typical eastern orientation, and suggest that Angkor Wat's alignment was due to its dedication to Vishnu, who was associated with the west.

Drawing on the temple's alignment and dimensions, and on the content and arrangement of the bas-reliefs, researcher Eleanor Mannikka argues that the structure represents a claimed new era of peace under King Suryavarman II: "as the measurements of solar and lunar time cycles were built into the sacred space of Angkor Wat, this divine mandate to rule was anchored to consecrated chambers and corridors meant to perpetuate the king's power and to honour and placate the deities manifest in the heavens above." Mannikka's suggestions have been received with a mixture of interest and scepticism in academic circles. She distances herself from the speculations of others, such as Graham Hancock, that Angkor Wat is part of a representation of the constellation Draco.

The oldest surviving plan of Angkor Wat dates to 1715 and is credited to Fujiwara Tadayoshi. The plan is stored in the Suifu Meitoku-kai Shokokan Museum in Mito, Japan.

Style

Angkor Wat as viewed from the side

Angkor Wat is the prime example of the classical style of Khmer architecture—the Angkor Wat style—to which it has given its name. By the 12th century Khmer architects had become skilled and confident in the use of sandstone (rather than brick or laterite) as the main building material. Most of the visible areas are of sandstone blocks, while laterite was used for the outer wall and for hidden structural parts. The binding agent used to join the blocks is yet to be identified, although natural resins or slaked lime has been suggested.

The temple has drawn praise above all for the harmony of its design. According to Maurice Glaize, a mid-20th-century conservator of Angkor, the temple "attains a classic perfection by the restrained monumentality of its finely balanced elements and the precise arrangement of its proportions. It is a work of power, unity, and style."

Architecturally, the elements characteristic of the style include: the ogival, redented towers shaped like lotus buds; half-galleries to broaden passageways; axial galleries connecting enclosures; and the cruciform terraces which appear along the main axis of the temple. Typical decorative elements are devatas (or apsaras), bas-reliefs, and on pediments extensive garlands and narrative scenes. The statuary of Angkor Wat is considered conservative, being more static and less graceful than earlier work. Other elements of the design have been destroyed by looting and the passage of time, including gilded stucco on the towers, gilding on some figures on the bas-reliefs, and wooden ceiling panels and doors.

Features

Outer enclosure

A view of the gates and west wall of the outer enclosure of Angkor Wat from across the moat

 

The Northern library

 

Ta Reach Statue at Angkor Wat, an Eight-Armed Vishnu.

The outer wall, 1,024 m (3,360 ft) by 802 m (2,631 ft) and 4.5 m (15 ft) high, is surrounded by a 30 m (98 ft) apron of open ground and a moat 190 m (620 ft) wide and over 5 kilometres (3 mi) in perimeter. The moat extends 1.5 kilometres from east to west and 1.3 kilometres from north to south. Access to the temple is by an earth bank to the east and a sandstone causeway to the west; the latter, the main entrance, is a later addition, possibly replacing a wooden bridge. There are gopuras at each of the cardinal points; the western is by far the largest and has three ruined towers. Glaize notes that this gopura both hides and echoes the form of the temple proper.

Under the southern tower is a statue known as Ta Reach, originally an eight-armed statue of Vishnu may have occupied the temple's central shrine. Galleries run between the towers and as far as two further entrances on either side of the gopura often referred to as "elephant gates", as they are large enough to admit those animals. These galleries have square pillars on the outer (west) side and a closed wall on the inner (east) side. The ceiling between the pillars is decorated with lotus rosettes; the west face of the wall with dancing figures; and the east face of the wall with balustered windows, dancing male figures on prancing animals, and devatas, including (south of the entrance) the only one in the temple to be showing her teeth.

The outer wall encloses a space of 820,000 square metres (203 acres), which besides the temple proper was originally occupied by the city and, to the north of the temple, the royal palace. Like all secular buildings of Angkor, these were built of perishable materials rather than of stone, so nothing remains of them except the outlines of some of the streets. Most of the area is now covered by forest. A 350 m (1,150 ft) causeway connects the western gopura to the temple proper, with naga balustrades and six sets of steps leading down to the city on either side. Each side also features a library with entrances at each cardinal point, in front of the third set of stairs from the entrance, and a pond between the library and the temple itself. The ponds are later additions to the design, as is the cruciform terrace guarded by lions connecting the causeway to the central structure.

Central structure

The temple stands on a terrace raised higher than the city. It is made of three rectangular galleries rising to a central tower, each level higher than the last. The two inner galleries each have four large towers at their ordinal corners (that is, NW, NE, SE and SW) surrounding a higher fifth tower. This pattern is sometimes called a quincunx and represents the mountains of Meru. Because the temple faces west, the features are all set back towards the east, leaving more space to be filled in each enclosure and gallery on the west side; for the same reason the west-facing steps are shallower than those on the other sides.

The central tower symbolizing the sacred Mount Meru

 

One of the four corner towers of Angkor Wat

 

A view of the outer gallery of Angkor Wat

Mannikka interprets the galleries as being dedicated to the king, Brahma, the moon, and Vishnu. Each gallery has a gopura at each of the points. The outer gallery measures 187 m (614 ft) by 215 m (705 ft), with pavilions rather than towers at the corners. The gallery is open to the outside of the temple, with columned half-galleries extending and buttressing the structure. Connecting the outer gallery to the second enclosure on the west side is a cruciform cloister called Preah Poan (meaning "The Thousand Buddhas" Gallery). Buddha images were left in the cloister by pilgrims over the centuries, although most have now been removed. This area has many inscriptions relating the good deeds of pilgrims, most written in Khmer but others in Burmese and Japanese. The four small courtyards marked out by the cloister may originally have been filled with water. North and south of the cloister are libraries.

Beyond, the second and inner galleries are connected to each other and to two flanking libraries by another cruciform terrace, again a later addition. From the second level upwards, devatas abound on the walls, singly or in groups of up to four. The second-level enclosure is 100 m (330 ft) by 115 m (377 ft), and may originally have been flooded to represent the ocean around Mount Meru. Three sets of steps on each side lead up to the corner towers and gopuras of the inner gallery. The very steep stairways represent the difficulty of ascending to the kingdom of the gods. This inner gallery, called the Bakan, is a 60 m (200 ft) square with axial galleries connecting each gopura with the central shrine, and subsidiary shrines located below the corner towers.

The roofings of the galleries are decorated with the motif of the body of a snake ending in the heads of lions or garudas. Carved lintels and pediments decorate the entrances to the galleries and to the shrines. The tower above the central shrine rises 43 m (141 ft) to a height of 65 m (213 ft) above the ground; unlike those of previous temple mountains, the central tower is raised above the surrounding four. The shrine itself, originally occupied by a statue of Vishnu and open on each side, was walled in when the temple was converted to Theravada Buddhism, the new walls featuring standing Buddhas. In 1934, the conservator George Trouvé excavated the pit beneath the central shrine: filled with sand and water it had already been robbed of its treasure, but he did find a sacred foundation deposit of gold leaf two metres above ground level.

Decoration

Integrated with the architecture of the building, and one of the causes for its fame is Angkor Wat's extensive decoration, which predominantly takes the form of bas-relief friezes. The inner walls of the outer gallery bear a series of large-scale scenes mainly depicting episodes from the Hindu epics the Ramayana and the Mahabharata. Higham has called these "the greatest known linear arrangement of stone carving". From the north-west corner anti-clockwise, the western gallery shows the Battle of Lanka (from the Ramayana, in which Rama defeats Ravana) and the Battle of Kurukshetra (from the Mahabharata, showing the mutual annihilation of the Kaurava and Pandava clans). On the southern gallery follow the only historical scene, a procession of Suryavarman II, then the 32 hells and 37 heavens of Hinduism.

Top: Devatas are characteristic of the Angkor Wat style. Bottom: The bas-relief of the Churning of the Sea of Milk shows Vishnu in the centre, his turtle avatar Kurma below, asuras and devas to left and right, and apsaras and Indra above.

On the eastern gallery is one of the most celebrated scenes, the Churning of the Sea of Milk, showing 92 asuras and 88 devas using the serpent Vasuki to churn the sea under Vishnu's direction (Mannikka counts only 91 asuras, and explains the asymmetrical numbers as representing the number of days from the winter solstice to the spring equinox, and from the equinox to the summer solstice). It is followed by Vishnu defeating asuras (a 16th-century addition). The northern gallery shows Krishna's victory over Bana (where according to Glaize, "The workmanship is at its worst").

Angkor Wat is decorated with depictions of apsaras and devata; there are more than 1,796 depictions of devata in the present research inventory. Angkor Wat architects employed small apsara images (30–40 cm or 12–16 in) as decorative motifs on pillars and walls. They incorporated larger devata images (all full-body portraits measuring approximately 95–110 cm or 37–43 in) more prominently at every level of the temple from the entry pavilion to the tops of the high towers. In 1927, Sappho Marchal published a study cataloging the remarkable diversity of their hair, headdresses, garments, stance, jewellery and decorative flowers, which Marchal concluded were based on actual practices of the Angkor period.

Construction techniques

Corridor

 

Decoration on the corner

The monument was made out of five to ten million sandstone blocks with a maximum weight of 1.5 tons each. The entire city of Angkor used far greater amounts of stone than all the Egyptian pyramids combined and occupied an area significantly greater than modern-day Paris. Moreover, unlike the Egyptian pyramids, which use limestone quarried 0.5 km (1⁄4 mi) away, the entire city of Angkor was built with sandstone quarried 40 km (25 mi) (or more) away. This sandstone had to be transported from Mount Kulen, a quarry approximately 40 kilometres (25 mi) northeast.

The route has been suggested to span 35 kilometres (22 mi) along a canal towards Tonlé Sap lake, another 35 kilometres (22 mi) crossing the lake, and finally 15 kilometres (9 mi) against the current along Siem Reap River, making a total journey of 90 kilometres (55 mi). However, Etsuo Uchida and Ichita Shimoda of Waseda University in Tokyo, Japan have discovered in 2011 a shorter 35-kilometre (22 mi) canal connecting Mount Kulen and Angkor Wat using satellite imagery. The two believe that the Khmer used this route instead.

Devata Sculpture on Wall at Angkor Wat

Virtually all of its surfaces, columns, lintels, and even roofs are carved. There are kilometres of reliefs illustrating scenes from Indian literature including unicorns, griffins, winged dragons pulling chariots as well as warriors following an elephant-mounted leader and celestial dancing girls with elaborate hairstyles. The gallery wall alone is decorated with almost 1,000 m² (11,000 sq ft) of bas reliefs. Holes on some of the Angkor walls indicate that they may have been decorated with bronze sheets. These were highly prized in ancient times and were a prime target for robbers.

While excavating Khajuraho, Alex Evans, a stonemason and sculptor, recreated a stone sculpture under 1.2 metres (4 ft), this took about 60 days to carve. Roger Hopkins and Mark Lehner also conducted experiments to quarry limestone which took 12 quarrymen 22 days to quarry about 400 tons of stone. The labour force to quarry, transport, carve and install so much sandstone must have run into the thousands including many highly skilled artisans. The skills required to carve these sculptures were developed hundreds of years earlier, as demonstrated by some artefacts that have been dated to the seventh century, before the Khmer came to power.

Angkor Wat in the present

Restoration and conservation

The restored head of a nāga beside an unrestored lion at the start of the causeway leading to the entrance of Angkor Wat. The contrast of restored and unrestored figures is deliberate. The major restoration of the causeway was first initiated in the 1960s by the French.

As with most other ancient temples in Cambodia, Angkor Wat has faced extensive damage and deterioration by a combination of plant overgrowth, fungi, ground movements, war damage and theft. The war damage to Angkor Wat's temples however has been very limited, compared to the rest of Cambodia's temple ruins, and it has also received the most attentive restoration.

The restoration of Angkor Wat in the modern era began with the establishment of the Conservation d'Angkor (Angkor Conservancy) by the École française d'Extrême-Orient (EFEO) in 1908; before that date, activities at the site were primarily concerned with exploration. The Conservation d'Angkor was responsible for the research, conservation, and restoration activities carried out at Angkor until the early 1970s, and a major restoration of Angkor was undertaken in the 1960s.

Work on Angkor was abandoned during the Khmer Rouge era and the Conservation d'Angkor was disbanded in 1975. Between 1986 and 1992, the Archaeological Survey of India carried out restoration work on the temple, as France did not recognise the Cambodian government at the time. Criticisms have been raised about both the early French restoration attempts and particularly the later Indian work, with concerns over damage done to the stone surface by the use of chemicals and cement.

In 1992, following an appeal for help by Norodom Sihanouk, Angkor Wat was listed in UNESCO's World Heritage in Danger (later removed in 2004) and World Heritage Site together with an appeal by UNESCO to the international community to save Angkor. Zoning of the area was set up to protect the Angkor site in 1994, APSARA was established in 1995 to protect and manage the area, and a law to protect Cambodian heritage was passed in 1996.

A number of countries such as France, Japan and China are currently involved in various Angkor Wat conservation projects. The German Apsara Conservation Project (GACP) is working to protect the devatas, and other bas-reliefs which decorate the temple, from damage. The organisation's survey found that around 20% of the devatas were in very poor condition, mainly because of natural erosion and deterioration of the stone but in part also due to earlier restoration efforts. Other work involves the repair of collapsed sections of the structure, and prevention of further collapse: the west facade of the upper level, for example, has been buttressed by scaffolding since 2002, while a Japanese team completed restoration of the north library of the outer enclosure in 2005.

A World Monuments Fund video on conservation of Angkor Wat

Microbial biofilms have been found degrading sandstone at Angkor Wat, Preah Khan, and the Bayon and West Prasat in Angkor. The dehydration- and radiation-resistant filamentous cyanobacteria can produce organic acids that degrade the stone. A dark filamentous fungus was found in internal and external Preah Khan samples, while the alga Trentepohlia was found only in samples taken from external, pink-stained stone at Preah Khan. Replicas have been made to replace some of the lost or damaged sculptures.

Tourism

See also: Tourism in Cambodia

 

Buddhist monks giving blessings to a tourist

Since the 1990s, Angkor Wat has become a major tourist destination. In 1993, there were only 7,650 visitors to the site; by 2004, government figures show that 561,000 foreign visitors had arrived in Siem Reap province that year, approximately 50% of all foreign tourists in Cambodia. The number reached over a million in 2007, and over two million by 2012. Most visited Angkor Wat, which received over two million foreign tourists in 2013, and 2.6 million by 2018.

The site was managed by the private SOKIMEX group between 1990 and 2016, which rented it from the Cambodian government. The influx of tourists has so far caused relatively little damage, other than some graffiti; ropes and wooden steps have been introduced to protect the bas-reliefs and floors, respectively. Tourism has also provided some additional funds for maintenance—as of 2000 approximately 28% of ticket revenues across the whole Angkor site was spent on the temples—although most work is carried out by teams sponsored by foreign governments rather than by the Cambodian authorities.

Tourists watching the sunrise in front of the reflecting pond at Angkor Wat

Since Angkor Wat has seen significant growth in tourism throughout the years, UNESCO and its International Co-ordinating Committee for the Safeguarding and Development of the Historic Site of Angkor (ICC), in association with representatives from the Royal Government and APSARA, organised seminars to discuss the concept of "cultural tourism". Wanting to avoid commercial and mass tourism, the seminars emphasised the importance of providing high-quality accommodation and services in order for the Cambodian government to benefit economically, while also incorporating the richness of Cambodian culture. In 2001, this incentive resulted in the concept of the "Angkor Tourist City" which would be developed with regard to traditional Khmer architecture, contain leisure and tourist facilities, and provide luxurious hotels capable of accommodating large numbers of tourists.

The prospect of developing such large tourist accommodations has encountered concerns from both APSARA and the ICC, claiming that previous tourism developments in the area have neglected construction regulations and more of these projects have the potential to damage landscape features. Also, the large scale of these projects have begun to threaten the quality of the nearby town's water, sewage, and electricity systems. It has been noted that such high frequency of tourism and growing demand for quality accommodations in the area, such as the development of a large highway, has had a direct effect on the underground water table, subsequently straining the structural stability of the temples at Angkor Wat.

Locals of Siem Reap have also voiced concern that the charm and atmosphere of their town have been compromised in order to entertain tourism. Since this local atmosphere is the key component to projects like Angkor Tourist City, the local officials continue to discuss how to successfully incorporate future tourism without sacrificing local values and culture.

At the ASEAN Tourism Forum 2012, it was agreed that Borobudur and Angkor Wat would become sister sites and the provinces sister provinces.

In 2020, the COVID-19 pandemic led to travel restrictions being introduced across the world, which had a severe impact on Cambodia's tourism sector. As a result, visitors to Angkor Wat plummeted, leaving the usually crowded complex almost deserted.