City workers discovered a pre-Columbian ossuary in San Andres Cholula, a city in the central Mexican state of Puebla, while completing a drainage project, the press reported.

The ossuary, which contains three complete human skeletons and 12 skulls, was found in a layer of soil dating back about 800 years, National Anthropology and History Institute, or INAH, officials told the press.

The remains may be from the Olmec-Chichimec culture, INAH experts said, adding that the bones appear to belong to members of one family who were buried over several generations.

The bones will be analyzed at an INAH laboratory while specialists continue to dig at the site, which was found about a month ago.

Specialists will try to gather more information at the site and a report will be issued in two months, the INAH said.