Cityscapes that have long remained buried in Cambodia’s heartland have been brought to light, thanks to a new series of airborne laser scans that penetrated the forest floor.

In a new report, due to be published today in the Journal of Archaeological Science, Australian archaeologist Damian Evans detailed the “incredible” discoveries unearthed through the Cambodian Archaeological Lidar Initiative (CALI).

The latest data from lidar – an airborne laser scanning technology attached to helicopters – from 2015 unveiled the entirety of Mahendraparvata, an ancient Khmer city that stretched up to 50 square kilometres around Siem Reap province’s Phnom Kulen. Only a fraction of the city had been uncovered in scans from 2012.

For Evans, a major breakthrough was the clarity lidar gave to Phreah Khan around Kampong Thom province’s Kampong Svay district – far from being sparsely inhabited, the data revealed a thriving city.

“We’d been looking for it unsuccessfully for a decade or more using every method at our disposal,” he said via email. “And then one day last year there it suddenly appeared on my screen, clear as day, looking just like the other cities built by the kings of the 12th century. Just incredible.

“The most amazing thing for me was the sheer length to which early Khmer societies went to transform the natural environments in which they lived.”

The new finds challenge dominant perceptions of the “collapse” of the Khmer Empire in the 15th century, often ascribed to a Thai sacking of the civilisation.

“The problem really is that the word ‘collapse’ has connotations of something that was sudden, dramatic and catastrophic . . . whereas the lidar shows fairly conclusively that this is not true,” Evans said.

The scans supported the theory of a gradual decline, rather than a sudden mass movement of hundreds of thousands of urbanites; evidence which Evans believes points to continued vitality for centuries at Angkor.

“The breakdown of the water management system at the end of the Angkor period had a significant role to play in a much more gradual demographic decline,” he added.

Dr Chen Chanratana, president of the Kerdomnel Khmer Foundation who holds a PhD in Archaeology from the Sorbonne, said the previously undiscovered finds were exciting and could shed light on urban living and water management for agriculture.

“It’s very import result for Cambodian people to think about the new theory of the collapse of the Khmer Empire and the move of the capital from one place to another,” specifically from Phnom Odong to Phnom Penh, he said via email. “This new result will challenge some of beliefs about Angkor history.”

Prak Sovannara, general director of the heritage department at the Ministry of Culture and Fine Arts, said the research helped reveal the “splendour of the civilisation” in the 12th and 13th centuries under Jayavarman VII.

“We have no plan to log those trees for the study since we can directly use the laser scan technology from the air,” Sovannara said.

Additional reporting Pech Sotheary