Archaeologists say they have discovered “an exceptional” burial site under an apartment building in Mexico City containing the remains of 12 dogs, animals that had a major religious and symbolic significance to the Aztec peoples of central Mexico.

Experts with Mexico’s National Institute of Anthropology and History, or INAH, said in a statement on Friday that this is the first time a group of dogs has been found buried together.

They have been found accompanying human remains or as part of an offering in a monument.

Aztecs believed dogs could guide human souls into a new life after death on earth.

Archaeologist Rocio Sanchez says the dogs were buried in a small pit between 1350 and 1520 AD, the heyday of the Aztec empire.