Archaeologists found pyramids, sports fields, causeways connecting districts and amphitheatres in the southeastern state of Campeche.

They uncovered the hidden complex - which they have called Valeriana - using Lidar, a type of laser survey that maps structures buried under vegetation.

They believe it is second in density only to Calakmul, thought to be the largest Maya site in ancient Latin America, the BBC reports.

The team discovered three sites in total, in a survey area the size of Scotland’s capital Edinburgh, “by accident” when one archaeologist browsed data on the internet.

“I was on something like page 16 of Google search and found a laser survey done by a Mexican organisation for environmental monitoring,” explains Luke Auld-Thomas, a PhD student at Tulane university in the US.

It was a Lidar survey, a remote sensing technique which fires thousands of laser pulses from a plane and maps objects below using the time the signal takes to return.

But when Mr Auld-Thomas processed the data with methods used by archaeologists, he saw what others had missed - a huge ancient city which may have been home to 30-50,000 people at its peak from 750 to 850 AD.

That is more than the number of people who live in the region today, the researchers say.

Mr Auld-Thomas and his colleagues named the city Valeriana after a nearby lagoon.

The find helps change an idea in Western thinking that the Tropics was where “civilisations went to die”, says Professor Marcello Canuto, a co-author in the research.

Instead, this part of the world was home to rich and complex cultures, he explains.

We can’t be sure what led to the demise and eventual abandonment of the city, but the archaeologists say climate change was a major factor.