For more than 600 years, the Khmer Empire dominated Southeast Asia, ruling over much of what is now Cambodia, Laos, Thailand, and Vietnam. The Khmer Empire is known today primarily for one of its most emblematic remnants, the temple complex Angkor Wat.

A man named Jayavarman II is generally thought to have been the first ruler of the Khmer Empire. In about 802, he consolidated his rule over neighboring peoples and declared himself chakravartin, or "universal ruler." It was from Mahendraparvata that Jayavarman ruled. The city was atop a mountain known as Phnom Kulen.

A multinational group of archaeologists announced the initial discovery of the ancient capital in 2012, combining old-fashioned ground-based explorations with air-based technology known as LiDAR. The acronym stands for light detecting and ranging. LiDAR shoots super-quick lasers out of an airplane and measures how long it takes the light to bounce off what's on the ground and hit cutting-edge detectors onboard the plane. The process is similar to the ways that bats use sonar to hunt. LiDAR mapping speed can reach 150,000 pulses a second.

After another set of expeditions in 2015, the archaeologists set about combining all of what they knew. The result was a very detailed map of a planned city that featured a grid stretching dozens of square miles and evidence of well planned excavation, such as a water basin carved out of existing bedrock, a process not repeated at Angkor, built later. That basin was not part of an irrigation system and was, in fact, left half-finished, the archaeologists said, suggesting that the city was the royal capital for only a short period of time. Among the other findings at the site was an inscription that corroborated this theory.

Use of LiDAR has increased in recent years. Among the other significant finds using the airborne technology have been these:

• In 2015, also in Cambodia, archaeologists concluded that Angkor Wat was much bigger in size and influence than previously thought.
• A team of archaeologists in Italy found evidence in 2015 of the oldest known Roman military camp, dating to 178 B.C.
• In 2018, a team of researchers found the ruins of 60,000 houses, palaces, elevated highways, and other evidence of Mayan civilization in Guatemala.