A mass grave discovered in Southern Mexico with the remains of 167 people is found to be an ancient burial ground, according to anthropologists.

The National Anthropology Institute said that the remains are 1,300 years old and date back to the eighth century. The Chiapas state prosecutor's office in a statement said that the site shared characteristics with other cemeteries that date from the years 700 to 1200, reported Reuters.

The skulls were found on the Nuevo Ojo de Agua ranch, some 20km (11 miles) from the Guatemalan border. Forensic experts initially thought that the skulls found in Chiapas, Mexico, were 50 years old, suggesting that they belonged to victims of the 1960-1996 civil war in Guatemala.

But they later found the skulls showed signs of a deformation typical of native communities dating back 1,000 years and more. The Maya people, who thrived in the region for nearly 2,000 years used planks to flatten and elongate the skulls of their children, reported BBC.

Researchers are now trying to determine the gender, age and the cause of their death.