Hundreds of strange metallic-looking spheres of unknown origin and purpose have been discovered by archaeologists exploring the ruins of an ancient Mesoamerican temple in Mexico, Discovery News reports. The spheres were uncovered by a camera-equipped robotic exploration rover on the floor of two previously sealed underground chambers in the Temple of the Feathered Serpent in the ancient city Teotihuacan, 30 miles away from Mexico City. They are thought to be at least 1,800 years old and are about 1.5 inches to 5 inches in size. Their cores are made up of clay and other unknown organic materials, while their surfaces are covered in pyrite, also known as "fool's gold," giving them a sparkling yellow coating.

"no one can establish their function."

The spheres are thought to be offerings of some kind, as the temple was used by priests, but for now, "no one can establish their function because it is an unprecedented discovery," said archaeologist Jorge Zavala in news release translated from Spanish, originally issued by the National Anthropology and History Institute of Mexico, which runs the site. Archaeologists are now performing imaging studies of the spheres, along with other artifacts found in the temple, to better understand what roles they played in ancient Mesoamerican society. Meanwhile, the scientists are hopeful about what they may find even deeper in the temple, potentially even the remains of the city's rulers.