The Temple of the Feathered Serpent is the third largest pyramid at Teotihuacan, a pre-Columbian site in central Mexico. Constructed in 200 AD, the six-level step pyramid was built using hundreds of enormous stone blocks that were majestically sculpted, harmoniously integrating the sculpture and the architecture in order to create this unique monument. The structure is notable partly due to the discovery in the 1980s of more than a hundred sacrifice victims found buried beneath the structure.

The pyramid takes its name from representations of the Mesoamerican "feathered serpent" deity which covered its sides. These are some of the earliest-known representations of the feathered serpent, often identified with the much-later Aztec god Quetzalcoatl.

Temple of the Feathered Serpent. Photo credit: Wikipedia

In May 2013, a team of archaeologists used a camera-equipped robot, to explore beneath the Temple of the Feathered Serpent . What they found was unprecedented – hundreds of gold-coloured metallic spheres scattered in two chambers which lie underneath the pyramid.

The mysterious spheres, which are gold in colour, range in size from 1.5 to 5 inches. They have an inner core of clay and are covered in a material called jarosite, which is formed by the oxidation of pyrite, a metallic ore.

"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.

According to George Cowgill, professor emeritus at Arizona State University and the author of several publications on Teotihuacan, the spheres would have shown up brilliantly in their time. Even the walls and ceiling of the chambers were covered with a mineral power composed of magnetite, pyrite and hematite which created a brightness in the areas.

As well as the spheres, archaeologists also found many other items including pottery and wooden masks covered in crystal, jade and quartz, indicating that the chambers were used by high-ranking people, priests or even rulers to perform rituals.

The next stage of the project will involve an exploration of three more chambers which archaeologists have seen through the robot cameras.

"The tunnel is in pristine condition, untouched for almost two millennia," said Ng Tze Chuen, an independent researcher who worked on the design of the Tláloc II-TC robot. "Can you can imagine what can be found inside?"

The team of researchers are hoping that the final chamber may lead to one of the most significant archaeological finds in Teotihuacan – the remains of those who ruled there.

By April Holloway