The experts continue their attempt to discover why Angkor suddenly collapsed, using a revolutionary technology called lidar to reveal the true scale and splendour of this abandoned megacity. Deep in the Cambodian jungle, they have discovered a sophisticated network of roads and canals that are the forgotten world of Angkor's greatest king, shedding new light on the dramatic events leading to the fall of the city.

A thousand years ago, the Khmer people of Cambodia built an empire and their capital was the great city of Angkor, with its centrepiece being Angkor Wat - a vast temple complex covering an area more than four times the size of the Vatican City. In the first of this two-part programme, an international team of archaeologists and scientists use revolutionary technology to reveal the true scale and extent of the lost metropolis and find out how its people lived and died.