SCIENCE / A FIND FOR ANTHROPOLOGISTS : Mexico City Yields More Clues to Past : A pre-Spanish skull, tablets are discovered by repairmen under a downtown mansion.

For a captured warrior in the Aztec Empire, the most honorable way to die was fighting. Tied to a giant stone, the prisoner would do battle against four gladiators at once. In death, he--or she--was decapitated, a sacrifice to the gods.

This, anthropologists say, may have been the fate of the Indian soul whose skull was unearthed in downtown Mexico City last month five feet beneath a colonial mansion that was undergoing restoration.

Nearby, diggers found what may be the key to the skull: six stone tablets depicting dismembered limbs, symbols of divine blood and acorns for the god Xipetotec, one of the many Aztec gods to whom sacrifices were made.

“This is the first time we have found something like this downtown,” said anthropologist Elsa Hernandez, who is in charge of the urban site. “The cranium is deformed. That is a characteristic of someone of high social class. As babies, their heads were bound with pieces of wood in the front and back until the bones gave way. It was considered beautiful.”

Anthropologists, who are just beginning to study the skull and tablets, are far from certain to which god the offering was made. But they consider the new find another clue to unraveling the mysteries of Mexico’s extensive and often grisly pre-Spanish past.

Spanish conquerors built Mexico City on the ruins of the Aztec capital, Tenochtitlan. The Aztec Templo Mayor, or Great Temple pyramid, was discovered in 1978, a block from the Spanish-built National Palace and the Roman Catholic cathedral. The Templo Mayor was the principal religious site, surrounded by lesser pyramids dedicated to minor gods.

The mansion at Argentina 12, where the skull and tablets were found, was built atop one of those. The temple was directly in front of the Templo Mayor and is believed to have been dedicated to either Coateocalli, the god of prisoners, or to Cihuacoatl, a serpent woman and goddess of land. The discovery may help anthropologists decide which one.

At the end of the 18th Century, Spanish tax collector Jose Francisco de Fagoaga y Arozqueta bought the land and commissioned Valencian sculptor Manuel Tolsa to build his three-story mansion.

Fagoaga’s elegant home was completed in 1805, five years before Mexico’s war of independence from Spain.

At the turn of the 20th Century, the Mexican government bought the colonial building to house its growing bureaucracy, using it for one of its ministries. Since then, the mansion has been in continuous use by various government offices. In 1988, it was turned over to the National Council for Culture and Arts.

In 1901, archeologists discovered the stairway to a pyramid beneath the mansion’s central patio. Soon afterward, they unearthed a carved stone jaguar, called Cuauhxicalli, with an opening in its back for offerings to the Aztec gods.

Mexico City, sitting on a dry lake bed prone to earthquakes, shakes like a soft bed under a restless sleeper. Its colonial buildings teeter, sink and crack. In 1985, while repairing the foundation of Argentina 12, workers discovered a stone eagle the size of a sheep.

The arts council has continued restoring the building amid the desks and paperwork. When fixing a crack last month, workers found the skull and tablets in the corner of a storeroom.

“These are pieces of the great mosaic that was the ceremonial center of Tenochtitlan,” Hernandez said. “They are pre-Hispanic information.”

Such digging goes on throughout downtown Mexico City, despite hordes of street vendors, office workers, shoppers and tourists. One gets the impression that all of the central city is sitting atop a pre-Spanish treasure chest: The Sun Temple was discovered beneath the cathedral in 1976; the Education Ministry building is being excavated now.

By law, anthropologists may examine all downtown work sites and renovations of colonial buildings. The subsoil is under the guardianship of the National Institute of Anthropology and History.

But sometimes they arrive too late. Workers renovating the San Agustin Church on Uruguay Street shoveled up a graveyard of Spanish viceroys before anthropologists could get to them.

“The workers don’t like us anthropologists very much because we interrupt their schedule,” Hernandez said. “But we have the right and obligation to go in. This is our history.”