An archeologist works over a skeleton at the site of a mass grave found in a ruined pyramid in the Tlateloco neighbourhood in Mexico City. The grave may hold the skeletal remains of the last holdouts among the Aztecs who fought the Spanish conquerors under Cortes. (AP Photo/Gregory Bull)

Archeologists digging in a ruined pyramid in downtown Mexico City say they found a mass grave that may hold the skeletal remains of the Aztec holdouts who fought conquistador Hernan Cortes.

The unusual burial site holds the carefully arrayed skeletons of at least 49 adults.

They were buried in the remains of a pyramid razed by the Spaniards during the 1521 conquest of the Aztec capital.

The pyramid complex, in the city's Tlatelolco square, was the site of the last Aztec resistance to the Spaniards during the months-long battle for the city.

Archeologist Salvador Guilliem is the leader of the excavation for Mexico's National Institute of Anthropology and History.

He said the Aztecs might have been killed during Cortes's war or during one of the uprisings that continued after the conquest.

Other sites found

Guilliem said many burial sites have been found in the area with the remains of people who died during epidemics that swept the Aztec capital in the years after the conquest and killed off much of the local population.

But those burials were mostly hurried, haphazard affairs in which remains were jumbled together in pits, regardless of age or gender.

The burial reported Tuesday is different.

The dead had many of the characteristics of warriors: All but four were young men, most were tall and several showed broken bones that had mended.

The men also were carefully buried Christian-style, lying on their backs with arms crossed over their chests, though many appear to have been wrapped up in large maguey cactus leaves, rather than placed in European coffins.

The mass grave contained evidence of an Aztec-like ritual in which offerings such as incense and animals were set alight in an incense burner, but Spanish elements including buttons and a bit of glass also were present.

Susan Gillespie, an archeologist at the University of Florida, said the grave was unusual , both because it was unlikely the Spanish would have bothered with such careful burial of Aztec warriors, and because the Indians themselves would have been more likely to cremate any honoured dead.

But Gillespie, who was not involved in the excavation, also noted that little is known about the period immediately following the fall of the city, when Cortes razed most pyramids and temples, then abandoned the largely destroyed metropolis.

He lived on the city's outskirts before returning to rebuild a Spanish-style city on the ruins.

It may have been in that interim period after Cortes left that the Aztecs returned to bury their dead, Guilliem said.