A Mayan city that had been lost for centuries beneath dense jungle in Mexico has been rediscovered by accident.
The settlement - which has been named Valeriana - was found by archaeologists studying an area of the Yucatan Peninsula.
Researchers believe the huge city could have been home to between 30,000 and 50,000 people at its peak between 750 and 850 AD, the BBC reports.
The settlement and its agricultural infrastructure cover a total area of more than 16.5sq km, and contain 6,764 structures of different sizes.
According to a new article published in journal Antiquity, it encompasses “two major hubs of monumental architecture 2km apart, linked by continuous dense settlement and landscape engineering”.
The researchers say the larger of Valeriana's two monumental precincts “has all the hallmarks of a Classic Maya political capital”.
They say it appears to contain “multiple enclosed plazas connected by a broad causeway; temple pyramids; a ballcourt; a reservoir formed by damming an arroyo (a seasonal watercourse), and curved, amphitheatre-like residential patios.
The discovery was made using ‘lidar’ - light detection and ranging - a technology that uses lasers to map and measure areas of vegetation.
Lidar was used to map an area of around 122sq km in 2013, as part of a forest monitoring project led by Mexico’s Nature Conservancy.
But the discovery of Valeriana was not made until Luke Auld-Thomas, a PhD student at Tulane University of Louisiana in the US, examined the lidar data on the internet around a decade later.
“I was on something like page 16 of Google search and found a laser survey done by a Mexican organisation for environmental monitoring,” Mr Auld-Thomas told the BBC.
He uncovered the hidden complex - which is believed to be “a populous and urban ancient Maya landscape”.
There are no known photographs of the remote, lost city.
"I've got to go to Valeriana at some point,” Mr Auld-Thomas told the BBC. “It's so close to the road, how could you not? But I can't say we will do a project there.
"One of the downsides of discovering lots of new Maya cities in the era of lidar is that there are more of them than we can ever hope to study.”
The discovery supports the idea that Mayans lived in complex cities rather than small, isolated village-like settlements, Elizabeth Graham, Emeritus Professor of Mesoamerican Archaeology at UCL, told the BBC.
Prof Graham, who was not involved in the research, said: "The point is that the landscape is definitely settled - that is, settled in the past - and not, as it appears to the naked eye, uninhabited or ‘wild’.”
The Maya civilisation was a Mesoamerican civilisation that began in around 250 AD. The city at Valeriana is believed to have “unravelled” in around 800 AD.
Mr Auld-Thomas told the BBC it appears the area “was just completely full of people at the onset of drought conditions and it didn't have a lot of flexibility left”. “And so maybe the entire system basically unravelled as people moved farther away.”
“The discovery of Valeriana highlights the fact that there are still major gaps in our knowledge of the existence or absence of large sites within as-yet unmapped areas of the Maya Lowlands,” said archaeologists in the Antiquity article.
