Mexican archaeologists in Tlalpan, a city south of Mexico City have found a 2,400 year old burial site where skeletons were laid in a spiral pattern. Researchers have never encountered such a burial before, and believe it may be part of a previously unknown ritual practice.

Excavations have been underway in Tlalpan since 2006, when an ancient city was discovered in the area. Archaeologists from Mexico’s National Institute of Anthropology and History (NIAH) found the remains about four feet underground, beneath a building of the Pontifical University of Mexico.

The remains, which include two females, a male, a child, and an infant, have intentionally deformed skulls and teeth. This cranial deformation—usually called head-binding—is typical for ancient indigenous people of this area. What’s particularly noteworthy is the True Detective-style arrangement of corpses.

It’s not clear yet how these people died, whether through natural causes or intentionally killings. But their skeletons’ orientations suggest that their deaths were part of an elaborate, mysterious ritual.

“We believe that it could be some interpretation of life, because individuals have different ages: There is a baby, a child, an infant, some young adults, adults, and an older adult,” Jimena Rivera, the director of the Project of Excavation and Archaeological Salvage at the Pontifical University of Mexico, told Noticieros Televisa

The settlement at Tlalpan was active during Mexico’s Pre-classical period, from 1,000 BC to 250 AD, long before the Aztec Empire, who were known for their brutal traditions of human sacrifice, came to dominate Mexico. As of yet, it’s unclear how this creepy burial fits in with those traditions, but it’s certainly intriguing.

Source: Instituto Nacional de Antropologia e Historia via Gizmodo