A tiny robot has made a momentous archaeological discovery deep under the famous Temple of Quetzalcoatl, near the Pyramid of the Sun in Mexico, it was announced on Monday.

Experts expected to find just one ancient chamber at the end of a stretch of 2,000-year-old unexplored tunnel at the Teotihuacan site. Instead, the remote-controlled vehicle has beamed back images of three mysterious caverns.

The three-foot-long investigator, named Tlaloc II-TC after the Aztec god of rain, was first lowered into the depths of the pyramid to check it was safe for human entry.

The temple is best known for the towering Pyramids of the Moon and the Sun.

The complex of pyramids, plazas, temples and avenues was once the center of a city of more than 100,000 inhabitants and may have been the largest and most influential city in pre-Hispanic North America at the time.

But nearly 2,500 years after the city was founded – and about 2,100 years after the Teotihuacan culture began to flourish there – very little is known about the identity of its rulers.

No depiction of a ruler, or the tomb of a monarch, has ever been found, setting the metropolis apart from other pre-Hispanic cultures that deified their rulers.

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