What we know and how
No Khmer building manual survives, and the inscriptions say little about technique. Knowledge of how Angkor Wat was built therefore comes from the structure itself: tool marks, unfinished areas, the quarries, the surrounding canals, and modern surveys and excavations. This leaves room for debate, and some parts of the story remain informed inference.
Two stones: laterite and sandstone
Two main building materials were used. Laterite, a reddish rock that is relatively soft when freshly cut and hardens on exposure, was available close to the site. It was used for the outer wall, for the cores and foundations of structures and for parts of the platforms. Sandstone was used for the visible architecture and the carving: galleries, towers, pillars, doorways and lintels.
The sandstone is generally traced to quarries in the Kulen hills, about 40 km to the northeast of Angkor Wat, although other sources may have contributed. This stone could be cut into large blocks and carved finely, but the distance and the weight of the blocks made transport the biggest logistical problem. The quantities involved were very large, running to many thousands of blocks of different sizes.
Moving the stone
The most likely method is that blocks were hauled on sledges or carts to the Kulen riverbanks and then floated on rafts or boats along waterways, and the last section was probably brought by canal. Angkor’s builders did dig canals and channels in the surrounding plain, and a number of them have been identified on aerial and LiDAR survey images. Recent research has suggested that a canal system linked the Kulen quarries to the Angkor area and that some canals ran close to Angkor Wat itself. The details of the route and the sequence are still debated, and not every proposal has been confirmed by excavation.
Elephants and human labour almost certainly played a part in hauling and lifting. Inscriptions from the Khmer period mention large temple workforces, but they do not give figures that could be used to estimate how many people worked on this specific building, and any numbers quoted in popular accounts should be treated cautiously.
Setting and carving the blocks
The sandstone blocks were cut to size, then fitted together with great precision, often without any mortar. Weight and tight joints kept them in place, with some blocks locked by tenons, dowels or small cut recesses. In some Khmer buildings, iron or other fittings may have been used, but the evidence varies from site to site.
The walls and towers were probably raised using earth ramps, wooden scaffolding, levers and pulleys. These methods can be inferred from partly finished buildings, though not every detail is known. Carving was normally done after the blocks were in place, which allowed scenes and patterns to run over several blocks and gave smooth joins. Unfinished reliefs at Angkor Wat show the stages of work: first the rough surface, then the outline, then the modelling and polishing.
Khmer builders also used the corbel arch, in which each layer of stone projects slightly beyond the one below until the sides meet. This method creates the long vaulted galleries and the stepped towers, and it explains why spaces inside the temple are narrow and tall, since the technique cannot span wide openings. It is a different approach from the true arch used in Roman aqueducts and bridges, and the contrast is a useful reminder that different traditions solved the same problems differently.
Foundations and the moat
Angkor Wat stands on a low, flat plain with a high water table, and a heavy stone building could settle unevenly. Investigations suggest that the main foundations involved a deep excavation filled with sand and layered with other materials, over which the platforms and laterite cores were built. Sand allows some movement and spreads loads, though it must stay damp to work well.
The moat probably played several roles. It is a symbol of the cosmic ocean in the mountain-temple model, and it also may have helped to regulate groundwater around the building, keeping the sandy fill stable. Some researchers have suggested this stabilising function, while others emphasise the symbolic and practical roles of water as a source and a boundary. The two ideas are not in conflict. Where sections of the western causeway and outer walls have subsided, the cause is generally linked to water changes and foundation movement, and restoration teams have had to deal with that problem.
Managing the water of Angkor
Angkor Wat was not isolated from a wider system. The Khmer kings built enormous rectangular reservoirs, called barays, such as the West Baray, which is roughly 8 km long, and the earlier East Baray. They also dug canals and diverted rivers such as the Siem Reap river to feed the system. Angkor Wat’s moat was linked into this network.
For many years, researchers argued that this system was mainly for irrigation and described Angkor as a hydraulic city. Others have pointed out that the reservoirs are also religious and royal monuments and that their practical effect on rice production is uncertain. Many scholars now see these roles as combined. The same works that stored water also displayed royal power, and they managed floods during the monsoon as well as dry periods. How much the system contributed to harvests, and how it coped when rainfall became erratic, are active research questions and tie into the debate about the end of Angkor as a capital.
The skill that remains
Compare this with other stone-building traditions that did not use mortar, such as the Inca builders who fitted irregular blocks at Cuzco stone walls: Khmer builders fitted rectangular blocks, and the result is visually different, though both depended on exact work. At Angkor Wat the result was a building that has stood for roughly nine centuries, with maintenance, in a climate that includes heavy rain, high humidity and growing roots. Its problems today, such as erosion, tree damage and subsidence, are a reminder of how much careful engineering it took to last this long.