Archaeologists, using a camera-equipped robot, have discovered hundreds of enigmatic, once-metallic spheres buried deep beneath an ancient pyramid in Mexico City. The mysterious spheres were found during an archaeological excavation 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. A World Heritage Site - the Mesoamerican ruins of Teotihuacan - represent one of the largest urban centers of the ancient world, 'Discovery News' reported. The pyramid-filled city, believed to have been established around 100 BC, had more than 100,000 inhabitants at its peak, but was abandoned for mysterious reasons around 700 AD. The archaeological dig 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. "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 Gomez Chavez, director of the Tlalocan Project, said. Researchers explored the tunnel with a remote-controlled robot called Tlaloc II-TC, which has an infrared camera and a laser scanner that generates 3D visualisation 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 from the entrance," Chavez said. The spheres lay in both 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. "This material is formed by the oxidation of pyrite, which is a metallic ore. It means that in pre-hispanic times they appeared as if they were metallic spheres. There are hundreds of these in the south chamber," said Chavez.