Nearly 900 years ago, the Khmer built Angkor Wat in what is now Cambodia, one of the largest religious monuments in Southeast Asia. It was built in the early of the 12th century, during the reign of King Suryavarman II.
The temple has towers, long galleries and enormous sandstone structures. It was built with no cranes, no trucks, no concrete mixers and no power drills, and nobody drew the plans in AutoCAD.
Archaeologists have found no lost machine or secret technology behind it. What the evidence shows is quarrying, transportation and construction organized on a massive scale.
First, They Needed a Lot of Stone
Sandstone was the main building material at Angkor. It appears in almost every monument there, alongside laterite and brick. Because the sandstone looks almost identical across the region, it is difficult to tell where individual blocks came from.
A 2007 study, "Consideration on the Construction Process and the Sandstone Quarries during the Angkor Period Based on the Magnetic Susceptibility", published in the Journal of Archaeological Science, found a way to trace them without damaging the stone.
Researchers used a handheld meter to measure the natural magnetism of around 50 blocks at each site. Stones from the same quarry tended to produce similar readings, allowing researchers to compare them across monuments.
Combined with an earlier study of Bayon-style monuments, the results pointed to seven sandstone quarries used during the Angkor period. Differences in the readings also helped researchers trace which quarry supplied different monuments and how sandstone use changed over time.
The sandstone came from the southeastern foot of Mount Kulen, about 40 kilometers northeast of Siem Reap, where several ancient quarries have been identified.
They Built a Supply Chain for the Stone
A 2013 study "Quarries and Transportation Routes of Angkor Monument Sandstone Blocks", identified more than 50 quarry sites clustered along a raised bank about 2.4 kilometers long.
The quarries also show how the work expanded over time. By comparing the stone from different pits and the height of the quarry walls, researchers found that quarrying appears to have started at the eastern end and gradually moved northwest.
Some northeastern quarries contain sandstone matching that used at Angkor Wat, but they are too small to have supplied the entire temple, suggesting that larger quarries may still be undiscovered.
The researchers believe the bank was used to transport the sandstone away from the quarries. They also traced a 34 kilometer route toward Angkor that combined roads, canals and rivers. The first 2 kilometers were a raised road, suggesting the blocks were moved over land before reaching a canal 20 to 30 meters wide.
Some sandstone blocks can still be found near the canal's beginning, supporting the idea that it was used to carry stone to Angkor. This route is more direct than an earlier theory that the blocks were taken to Tonle Sap and then moved about 90 kilometers up the Siem Reap River.
Once the heavy sandstone blocks reached the site, the Khmer still had to put them in place.
Christophe Pottier, an archaeologist and architect who specializes in Angkor, suggested that workers could have used wooden rollers to move the blocks over short distances, while scaffolding, levees and pulleys may have helped position them during construction. None of these systems survives intact at the site, so the exact methods remain uncertain.
Angkor Wat Wasn’t Built in One Go
Angkor Wat is often described as a single grand project built under King Suryavarman II in the early 12th century.
But a 2025 study "Using Magnetic Susceptibilities of the Sandstone Blocks to Determine the Construction Period of the Revetment of the Surrounding Moat of the Angkor Wat Temple, Cambodia", published in Archaeological Discovery, suggests that at least some parts of the temple complex may have been built later.
Researchers compared the natural magnetism of the stone lining the surrounding moat with stones from the temple and other Angkor monuments.
The stone inside Angkor Wat gave generally higher readings, while much of the moat's stonework was closer to sandstone from the Bayon period in the late 12th to early 13th century. The researchers therefore concluded that most of the lining was probably added after the main temple was built.
The western stretch of the moat, directly in front of the main entrance, is an exception. Its stonework appears to date from around the same period as the temple and is better built than the rest, which suggests the lining was added in at least two stages.
The researchers stress that this does not mean the moat itself was dug later. The moat likely already existed, while its stone-lined banks were added or rebuilt over time.
What We Still Don't Know
The studies show where Angkor's sandstone came from, how quarrying shifted over time and how the blocks probably reached the temples. They say little about how individual blocks were lifted into place, and no account of that survives from the period.
What they do establish is a link between quarries and construction. Different monuments drew on different quarries, and a canal and embankment system probably carried stone from Mount Kulen toward them. Most of the moat's stone lining was probably added after the main temple, which suggests Angkor Wat took shape in stages.
The size of the labor force remains unknown, and larger quarries may still be waiting to be found.
References:
Uchida, E., Cunin, O., Suda, C., Ueno, A., & Nakagawa, T. (2007). Consideration on the construction process and the sandstone quarries during the Angkor period based on the magnetic susceptibility. Journal of Archaeological Science, 34(6), 924-935. https://doi.org/10.1016/j.jas.2006.09.015
Uchida, E., & Shimoda, I. (2013). Quarries and transportation routes of Angkor monument sandstone blocks. Journal of Archaeological Science, 40(2), 1158-1164. https://doi.org/10.1016/j.jas.2012.09.036
Uchida, E., Kobayashi, Y., Sasaki, S., Kuriyama, K., & Saitoh, Y. (2025). Using magnetic susceptibilities of the sandstone blocks to determine the construction period of the revetment of the surrounding moat of the Angkor Wat Temple, Cambodia. Archaeological Discovery, 13, 99-113. https://doi.org/10.4236/ad.2025.132006
