A 16th Century altar and a pot containing human ashes and 13 incense burners have been discovered around 13 feet below ground level in Mexico City’s Plaza Garibaldi.

According to a BBC report, the excavation was carried out by Mara Becerra of Mexico’s National Institute of Anthropology and History and her colleagues.

The altar, thought to have been used to mark the cycles of life with rituals, has been dated to sometime between 1521, when the Spanish conquered Tenochtitlan, and 1610. Becerra thinks the altar was placed in a courtyard within the home of a Mexican family in order to hide it from the Spanish rulers.

The structure had a large room connected by a corridor to five smaller rooms, one of which is thought to have been a kitchen.