Mexico City - Archaeologists have found an ancient Maya city that remained hidden for centuries in the rain forests of eastern Mexico, a discovery in a remote nature reserve they hope will yield clues about how the civilisation collapsed around 1 000 years ago.The team, led by Ivan Sprajc, associate professor at the Slovenian Academy of Sciences and Arts, found 15 pyramids - including one that stands 23m tall - ball courts, plazas and tall, sculpted stone shafts called stelae.They named the city Chactun, meaning "Red Rock" or "Large Rock". Sprajc said it was likely slightly less populous than the large ancient Maya city of Tikal in Guatemala, and could have been home to as many as 30 000 or 40 000 people, though further research is necessary to determine an exact estimate.Chactun likely had its heyday during the late Classic period of Maya civilisation between 600 and 900CE (Common Era), Sprajc said.The team's research was approved by the Mexican National Institute of Anthropology and History and funded by the National Geographic Society and two European companies.VisitorsSprajc said the site - which covers 22ha and lies 120km due west of Chetumal - is one of the largest found in the Yucatan's central lowlands. The nearest settlement to the ruins is the small town of Xpujil, around 25km away."The whole site is covered by the jungle," he said in Spanish.While the site was unknown to the academic community, Sprajc found evidence that other people had been to the site as recently as 20 or 30 years ago, but not since."Lumberjacks and gum extractors were certainly already there, because we saw cuts on the trees," Sprajc said. "What happened is they never told anyone."While reviewing aerial photographs taken by the National Commission for the Knowledge and Use of Biodiversity 15 years ago to monitor the nature reserve, Sprajc and his team saw suggestions of ruins and marked the co-ordinates.They then spent three weeks clearing a 16km path through the jungle to reach the site. After mapping the site for six weeks and documenting the monuments, they blocked the path before leaving to prevent access.The presence of multiple ball game courts is an indication that Chactun was a very important city, Sprajc said. It was likely abandoned around the year 1 000, probably due to demographic pressure, climate change, wars and rebellions.Maya calendarHe hopes the find could shed new light on relations between different regions of the Maya empire during that period.The Maya civilisation was one of the most advanced in the pre-Columbian Americas and ruled over large swaths of the Yucatan, Belize, Guatemala and Honduras at its height.Tikal, which was first mapped by archaeologists in the late 19th century, had a population estimated at up to 90 000.In December, thousands of people travelled to the Yucatan to celebrate a new cycle in the Maya calendar amidst fears that the Maya had actually predicted that 21 December would mark the end of the world.