But back in the 1860s Angkor Wat was virtually unheard of beyond local monks and villagers. The notion that this great temple was once surrounded by a city of nearly a million people was entirely unknown. It took over a century of gruelling archaeological fieldwork to fill in the map. The lost city of Angkor slowly began to reappear, street by street. But even then significant blanks remained. Then, last year, archaeologists announced a series of new discoveries – about Angkor, and an even older city hidden deep in the jungle beyond.
An international team, led by the University of Sydney’s Dr Damian Evans, had mapped 370 sq km around Angkor in unprecedented detail – no mean feat given the density of the jungle and the prevalence of landmines from Cambodia’s civil war. Yet the entire survey took less than two weeks. Their secret? Lidar – a sophisticated remote sensing technology that is revolutionising archaeology, especially in the tropics. Mounted on a helicopter criss-crossing the countryside, the team’s lidar device fired a million laser beams every four seconds through the jungle canopy, recording minute variations in ground surface topography.