MEXICO CITY (AP) — Mexican archaeologists believe they have found the main trophy rack of sacrificed human skulls at Mexico City's Templo Mayor Aztec ruin site.

Racks known as "tzompantli" were where Aztecs displayed the severed heads of sacrificial victims on wooden poles pushed through the sides of the skull.

But archaeologists at Mexico's National Institute of Anthropology and History said Thursday that this one was different. Part of the platform where the heads were displayed was made of rows of skulls mortared together roughly in a circle. All the skulls were arranged to look inward toward the center of the circle, but experts don't know what was at the center.

The find was made between February and June under the floor of a colonial-era house in downtown Mexico City.