• A local, slice-of-life story from a Monitor correspondent.

In the middle of Mexico City’s historical downtown, where the modern bustle leaves most visitors in a daze, archaeologists have unearthed something altogether more serene: a potential clue in their quest to find the long sought-after tombs of Aztec emperors.

This fall, amid ongoing excavation at the Templo Mayor site, where one of the main temples of the ancient capital, Tenochtitlan, once stood, they discovered a 500-year-old platform 45 feet in diameter and decorated with 19 sculptures of serpent heads. Tenochtitlan, built in the middle of Lake Texcoco, was the heart of Aztec civilization, whose influence spread across Mesoamerica until the 16th century.

The finding is part of a five-year effort to locate the tombs in the ancient site, which, now in the heart of Mexico’s capital, was paved over by the Spanish invaders in 1521.

Archaeology work began at the Templo Mayor in earnest after 1978, when workers from the electric company accidentally dug up a pre-Hispanic monolith 10.6 feet in diameter, which was later excavated and identified as Coyolxauhqui, the moon goddess, and dates back to the end of the 15th century.

Today, some 7,000 pieces have been uncovered. But an emperor’s tomb would be a critical find, and the ceremonial platform is an important step toward understanding the rituals of the Aztecs, says Alfonso de Maria y Campos, director general of Mexico’s National Institute of Anthropology and History.

The finding is currently off limits to the public.