Scientists with the Mexican government announced Wednesday the discovery of three new chambers at the end of a tunnel under the ancient city of Teotihuacan. The tunnel was discovered in 2003 beneath the popular tourist destination just outside today’s Mexico City and is among the most important finds in the lost city’s history.

In a press briefing at the National Museum of Anthropology in Mexico City, Mexican archeologists say that the new rooms contained thousands of objects, including carved statues, rubber balls, jade from Guatemala and a wooden box of shells. Beyond some traces of skin, however, no bodies have been discovered, although archaeologists have hypothesized that the site holds a burial chamber, perhaps still buried in the soil. “Just before the chambers is where we found very important offerings—a lot of them—alongside many objects," says Sergio Gomez, who directs the excavation project.

Archeologists know very little about mountain city of Teotihuacan. The tunnel, discovered 11 years ago under the Temple of the Feathered Serpent at the heart of the ancient metropolis, is the latest piece in a puzzle dating back to before Europeans arrived in the New World. “These findings are very important, both for the quantity and the quality of materials being discovered,” wrote George Cowgill, a professor at Arizona State University in Tempe who directs a research center at Teotihuacan, in an e-mail. It will probably take years of analysis to truly understand the significance of each object and the assemblage, he added.

As a city, Teotihuacan began around 150 B.C. and collapsed sometime in the seventh century A.D. During that time it was probably the most powerful city in all of North America, dominating even the Classic Maya, who were their lowland contemporaries far to the east in what is now southern Mexico and Guatemala.

The inhabitants of Teotihuacan, unlike the Maya, did not have a system of writing and thus we know very little about how they lived or ran their city. For instance, archeologists debate their political structure: One side envisions a single omnipotent ruler whereas the other sees a joint rule shared by four competing factions.

Unfortunately, Teotihuacan has neither images of its kings nor royal burials, although scientists have found numerous high-ranking nobles. The discovery of a royal burial under the Temple of the Feathered Serpent might upend everything known about the city.

The tunnel itself was discovered when a heavy rainstorm exposed a shaft that led to a spot about halfway down its length. The shaft’s purpose remains a mystery but scientists believe the tunnel had a ceremonial purpose, and it is possible that the shaft was used for astronomical purposes.

Over the next decade Gomez’s team dug out the tunnel and found numerous offerings. Their work culminated in 2013 with the discovery of a series of two chambers on either side of the tunnel near the end filled with pyrite mirrors and strange crystal spheres. After that the tunnel dropped below the water table. "The water has made our work move slower, however the large quantity of water below has enabled the preservation of materials like wood, rubber and even skin fragments," Gomez says.

He and his team announced Wednesday that three more chambers lay beyond the initial two, oriented in a sort of cross just a few dozen feet down the tunnel. In and around those chambers he found more puzzling objects, including a wooden box filled with shells imported from the ocean and carved by stone tools.

In addition, there were four 60-centimeter-tall jade statues, rubber balls and jaguar remains. They also report finding fragments of skin, although they can’t be sure yet if it is human. Human or not, there are no obvious burials in any of the chambers but that does not mean that the quest for a Teotihuacan burial is over. “These could be funerary offerings but I wonder if they might be remains of a huge feast—a feast that might have been part of a great funerary and sacrificial ceremony, especially considering the large number of rather plain jars,” Cowgill wrote. He added that other objects in the chamber reinforce the importance of women in Teotihuacan society as well as the long reach of their trade.

Gomez’s team is in the process of excavating the rooms down to the floors and it is possible there are nobles buried in the detritus or even below the chamber floors. He expects the work to continue and remains optimistic that a body will be found. “It's very exciting because it corroborates our hypothesis that this could be an offering for something more important that lies beneath. And the hypothesis is that there is a burial site but we won’t know for sure until next year."