Angkor

Angkor's scale defeats first attempts at comprehension. Angkor Wat — the structure most people picture when they hear the name — is already larger than any religious building in the world, a 402-acre complex of galleries, towers, and reflecting pools aligned to astronomical precision on a north-south axis. But Angkor Wat is the centrepiece of a city, not its entirety. The city that surrounded it, only fully mapped in the twenty-first century by LiDAR surveys that could see through the dense forest canopy, turns out to have covered something in the range of 1,000 square kilometres — roughly the area of modern Singapore — and to have been sustained by a hydraulic management system of extraordinary sophistication that moved, stored, and distributed water on a landscape scale that has no close parallel in the pre-industrial world.

The people who built Angkor were the Khmer, and the civilisation they constructed between the ninth and fifteenth centuries CE was the dominant power of mainland Southeast Asia. Their kings were god-kings — devaraja — who expressed their divinity through the construction of temple-mountains aligning the royal capital with Mount Meru, the cosmic mountain at the centre of the Hindu universe. Each major temple is therefore not merely an architectural achievement but a cosmological statement, a claim about the king's relationship to the divine that was expressed in sandstone with extraordinary permanence.

802 CE — The God-King Declares Himself

Jayavarman II climbs Phnom Kulen hill north of the future capital site in 802 CE and performs a ritual that declares him the universal monarch of the Khmer people — a ceremony that simultaneously inaugurates the Khmer Empire and establishes the model of divine kingship that will define Angkor's political culture for the next six centuries. He establishes his capital in the area that will become Angkor, beginning the process of hydraulic engineering — reservoirs, canals, channels — that transforms a landscape of seasonal monsoon flooding into one of the most productive agricultural systems in Southeast Asia.

9th to 11th Century CE — The City Takes Shape

Successive rulers construct temple complexes on the site, each king establishing his own mountain-temple as a statement of legitimacy and a vehicle for royal merit. Indravarman I builds the first large baray — an artificial reservoir — at Lolei, establishing the hydraulic model that will be expanded by every subsequent ruler. Yasovarman I builds the East Baray, 7 kilometres long and 1.8 kilometres wide, the largest water storage structure in the ancient world at the time of its construction, and moves the capital to the site that will become Angkor Thom. The landscape is being actively engineered at a scale that requires the coordination of tens of thousands of workers and a sophisticated understanding of hydrology, gradient, and soil behaviour.

1113 to 1150 CE — Angkor Wat

Suryavarman II commissions the structure that will be the architectural culmination of everything Khmer civilisation has been working toward. Angkor Wat is dedicated to Vishnu rather than the Shiva cult that had dominated earlier Khmer royal patronage, and it is oriented to the west — the direction of the setting sun and of death in Hindu cosmology — raising the possibility that it was conceived from the beginning as a funerary monument as well as a religious one. Its galleries, 800 metres in length on each side, are covered with the longest continuous bas-relief narrative in the world, depicting scenes from the Hindu epics and the military campaigns of Suryavarman II himself. The precision of its astronomical alignments — the sun rises directly over the central tower at the spring equinox, and the towers cast shadows that align with carved figures at specific dates — implies a level of planning and astronomical sophistication that would not be out of place in a modern engineering project.

1181 to 1219 CE — The Empire at Its Height

Jayavarman VII, the most prolific builder in Khmer history, constructs Angkor Thom — the great city — as his capital, enclosing nearly 10 square kilometres within stone walls and moats and placing the Bayon temple, with its 216 carved faces of the Bodhisattva Avalokitesvara, at the geometric centre. He builds Ta Prohm, Preah Khan, Banteay Kdei, and dozens of subsidiary temples, hospitals, and rest houses along the road network. The Cambodia of his reign has converted to Mahayana Buddhism, which represents a significant religious shift from the Hindu traditions that preceded him, but the temple-mountain model survives the conversion intact. The population of Greater Angkor during this period, recent demographic modelling suggests, may have been close to 750,000 — a figure that would make it one of the largest urban agglomerations on earth at the time.

13th to 15th Century CE — Decline and Abandonment

The mechanisms of Angkor's decline are still debated. The conventional account points to military pressure from the Thai kingdom of Sukhothai and its successor Ayutthaya, which raided the capital repeatedly in the fourteenth and fifteenth centuries. More recent research adds a second factor: the hydraulic system that had sustained the city was showing signs of stress, with evidence of canal blockages, flood damage to key infrastructure, and possibly climate-driven changes in monsoon rainfall patterns. The combination of external military pressure and internal hydraulic failure may have made the city increasingly difficult to sustain, leading to a gradual southward shift of political and economic activity toward Phnom Penh and the Mekong delta trade routes.

1860 to 1990s — Western Discovery and French Conservation

Henri Mouhot's accounts of Angkor, published in 1863, introduced the site to a European audience — though the local Khmer population had never ceased to regard Angkor Wat as a functioning religious site, and monks had been resident there continuously for centuries. The French colonial administration established the École française d'Extrême-Orient, which conducted the first systematic conservation work at Angkor from 1908 onward. The anastylosis method — disassembling collapsed structures and reassembling them correctly — was pioneered at Angkor and remains a standard conservation technique. The political upheavals of the twentieth century, including the Khmer Rouge period (1975–1979), disrupted but did not entirely halt conservation work, though the site suffered looting and some structural damage during the civil conflict period.

1992 — World Heritage and the In Danger List

Angkor was inscribed on the UNESCO World Heritage List in 1992 — simultaneously inscribed on the List of World Heritage in Danger, reflecting the site's condition after years of conflict and limited institutional capacity. An international coordinating committee for the safeguarding of Angkor was established, bringing together conservation teams from France, Japan, Germany, India, China, the United States, and other countries, each working on different parts of the site. The management framework that resulted was unprecedented in its scale and multilateral complexity. The site was removed from the Danger List in 2004 — a recognition of the progress made, though the underlying challenges had not been resolved.

Today — Tourism, Groundwater, and the LiDAR Revolution

Aerial LiDAR surveys conducted between 2012 and 2015 revealed that the urban footprint of Greater Angkor was significantly larger than a century of on-the-ground archaeology had established — extending far beyond the monumental core and incorporating agricultural zones, residential areas, and hydraulic infrastructure that had been invisible beneath the forest canopy. The surveys also revealed the extraordinary complexity and sophistication of the hydraulic system, identifying canals, channels, and water management structures that had not been documented before. This research transformed scholarly understanding of Angkor's scale and its hydraulic engineering, and it has direct implications for conservation planning.

Angkor carries an At Risk classification — a site where significant and measurable threats are active, where the trajectory is concerning, but where the situation has not yet crossed into irreversible damage at scale.

Groundwater Depletion is the most technically complex and potentially severe threat. The hotels, guesthouses, and tourism infrastructure that have grown up around Siem Reap over the past three decades draw water from wells that tap the same aquifer that underlies the monument foundations. When groundwater levels drop, the sandstone foundations of the temples lose the buoyant support that the saturated soil provided, and differential settlement — uneven sinking — begins. The damage this causes to masonry structures designed for stable foundations is gradual, cumulative, and difficult to reverse once it reaches a certain point. Research using precision levelling and GPS monitoring has documented measurable movement at several major structures.

Vegetation and Structural Biology present a challenge of particular poignancy at temples like Ta Prohm, where enormous silk-cotton trees have grown through and around the structures for centuries. The trees are simultaneously part of the site's atmosphere — one of the most haunting visual experiences in Southeast Asian heritage — and the cause of structural damage as root systems penetrate masonry joints and expand seasonally. Managing this tension between the conservation value of stabilising the trees and the structural damage they cause is a dilemma that has produced no fully satisfactory solution.

Tourism Pressure at Scale has concentrated visitor impact on a small number of iconic structures — Angkor Wat, the Bayon, Ta Prohm — while leaving hundreds of secondary sites with minimal conservation attention. The wear patterns on sandstone balustrades and carved surfaces from millions of hands are visible and measurable. The carbon dioxide and humidity generated by dense crowds within enclosed gallery spaces creates an atmospheric microenvironment that accelerates biological growth on carved surfaces. The economic rationale for managing visitor numbers at flagship sites runs directly against the economic interests of the tourism infrastructure that the site has supported.

Hydraulic System Deterioration — the ancient reservoirs and canal systems that once managed water across the landscape are no longer maintained as functional systems. Their condition affects the hydrology of the landscape, the water table beneath the monuments, and the flood dynamics that affect low-lying temple complexes. Research into the ancient hydraulic system has demonstrated that it was, at its height, capable of managing monsoon water at a landscape scale — storing excess water in the dry season, distributing it for agriculture and domestic use, and moderating the flood pulses that would otherwise inundate the lower-lying areas of the urban fabric. Its current state, partially silted, partially collapsed, partially obscured by vegetation, represents a significant reduction in its capacity to perform those functions.

The LiDAR surveys of 2012–2015, conducted by the Greater Angkor Project and Cambodian authorities, represent the single most significant advance in Angkor scholarship since systematic archaeological work began in the early twentieth century. By producing detailed elevation models of the landscape beneath the forest canopy, the surveys revealed the full extent of the urban infrastructure and established that Angkor was, at its height, not merely a temple complex surrounded by settlements but one of the most densely and deliberately engineered urban landscapes in the pre-industrial world. The hydraulic system, seen in its full extent for the first time, turns out to be a civilisation-scale water management infrastructure whose design logic has taken researchers years to begin to fully understand.

Archaeological work at the site has produced increasingly detailed chronologies of the construction phases of individual monuments, revealing that structures which appear unified were in fact built and modified over periods of decades or centuries, with different building campaigns visible in the variation of stone quality, carving style, and structural technique. Research into the labour systems that produced the monuments — drawing on inscriptions, comparative ethnographic data, and the logistical modelling of construction timelines — has established that the temples were the product of a complex economy of merit, obligation, and skilled craft specialisation rather than simple forced labour.

The climate science applied to Angkor's decline has produced some of its most significant results through the analysis of tree ring records from trees growing in or near the site, which have revealed evidence of two extended drought periods — one in the mid-fourteenth century and one in the early fifteenth century — that correlate with and may have contributed to the periods of political instability that preceded the capital's abandonment.

Angkor Wat and the monuments of the inner zone will not collapse. They are the subject of continuous conservation attention from multiple international teams with the expertise and resources to maintain structural stability indefinitely. The risk to Angkor is not the loss of its most famous structures but the gradual degradation of the much larger ensemble — hundreds of secondary temples, the hydraulic infrastructure, the landscape context — that gives the core monuments their meaning.

Groundwater depletion is the threat with the most serious long-term structural implications, because it operates below the surface and its effects are not visible until significant damage has already occurred. If extraction from the Siem Reap aquifer continues at current rates, the differential settlement it is causing will eventually produce structural failures that conservation work cannot reverse.

Angkor survived abandonment, civil war, and a century of international neglect. Its surviving fabric is a testament to the quality of its original construction. But stone can be destabilised by subsidence, carved by biological growth, and physically worn by millions of feet in ways that no amount of subsequent care can fully undo. The window for managing these threats before they become irreversible is not closed. But it requires decisions — about groundwater regulation, about tourism management, about conservation resourcing — that have been deferred for long enough.