Hundreds of mysterious spheres lie beneath the Temple of the Feathered Serpent, an ancient six-level step pyramid just 30 miles from Mexico City.
The enigmatic spheres were found during an archaeological dig using a camera-equipped robot at one of the most important buildings in the pre-Hispanic city of Teotihuacan.
"They look like yellow spheres, but we do not know their meaning. It's an unprecedented discovery," said Jorge Zavala, an archaeologist at Mexico's National Anthropology and History Institute.
The Mesoamerican ruins of Teotihuacan, a World Heritage Site, represent one of the largest urban centers of the ancient world. Thought to have been established around 100 B.C., the pyramid-filled city had more than 100,000 inhabitants at its peak, but was abandoned for mysterious reasons around 700 A.D. -- long before the Aztecs arrived in the 1300s.
The excavation at the temple focused on a 330-foot-long tunnel which runs under the structure. The conduit was discovered in 2003 when heavy rain uncovered a hole a few feet from the pyramid.
Exploring the tunnel, which was deliberately filled with debris and ruins by the Teotihuacan people, required several years of preliminary work and planning.
"Finally, a few months ago we found two side chambers at 72 and 74 meters (236 and 242 feet) from the entrance. We called them North Chamber and South Chamber,” archaeologist Sergio Gómez Chávez, director of the Tlalocan Project, told Discovery News.
The archaeologists explored the tunnel with a remote-controlled robot called Tlaloc II-TC, which has an infrared camera and a laser scanner that generates 3D visualization of the spaces beneath the temple.
"The robot was able to enter in the part of the tunnel which has not yet been excavated yet and found three chambers between 100 and 110 meters (328 and 360 feet) from the entrance," Gómez Chávez said.
The mysterious spheres lay in both the north and south chambers. Ranging from 1.5 to 5 inches, the objects have a core of clay and are covered with a yellow material called jarosite.