An exciting archaeological discovery in Mexico City is shaking things up for pre-Hispanic historians. Salvador Guilliem Arroyo announced that his team had uncovered ancient ruins in Tlatelolco, a neighborhood in the center of the sprawling capital. Believed to be built between 800 and 1,100 A.D., the site’s Templo Mayor (Main Temple) could be 225 to 525 years older than any other previously-known Aztec remnant. If the teac can corroborate these initial findings, the discovery will necessitate revision of the established timeline for the development of the Aztec civilization.

Guilliem Arroyo’s team began investigation of the Tlatelolco ruins in 1992, but work was suspended in 1993 after an earthquake damaged the site. To aid in accessing the ruins, the workers used a tunnel that reached up to seven meters (about 21 feet) in depth, largely constructed by Mexica peoples. The Tlatelolco site includes a complex used as a religious center dedicated to the military elite.

Previous research determined that Tlatelolco was founded in 1325, the same time as the Aztec Empire’s capital of Tenochtitlán, what is today Mexico City’s historic downtown. The great city was destroyed in 1521 after being conquered by Hernán Cortés’ small army. One of the first projects of the Spanish conquistadors was to construct a cathedral—which they did directly on top of Tenochtitlán’s Templo Mayor. This pyramid has been partially recovered, although full exploration would compromise the cathedral, something that no one is willing to do. The new evidence from Tlatelolco seems to place that city earlier than Tenochctitlán, and will most likely spur further investigation of the latter.