Mexico city, Aug 18 (IANS): Archaeologists have uncovered 1,000-year-old circular earthen pits built into the ground at an ancient ceremonial complex in central Mexico likely to have been used to process corn.

Four small pits dating to 1,000-1,350 A.D were discovered at the Old Tehuacan ceremonial complex in Puebla state "could be evidence of pre-Hispanic nixtamalisation work," Xinhua news agency reported, citing researchers at the National Institute of Anthropology and History.

Nixtamalising corn requires soaking the kernels in an alkaline solution, usually made with lime water, before hulling and grinding them for cooking.

The pits were reportedly located near kitchen areas, where comals (flat griddles used to heat food) were found. Each pit, with a diameter of 60 cm, was made from a mixture of clay and lime and could hold up to five litres of water.

Researchers ruled out the possibility that the pits could have been used to collect and distribute water, since they were separated from the site's complex rainwater gathering system.

In that system, rainwater was stored in giant cisterns capable of holding up to 20,000 litres of water and channelled throughout the site via a network of canals that ran along the main plazas.