Beneath the imposing temples and pyramids of Mexico’s ancient city of Teotihuacan, an intriguing but toxic mystery lurks — shimmering pools of liquid mercury.

Teotihuacan, a pre-Columbian urban center dating back to 100 BC, was one of the largest cities in the ancient world, boasting a populace of over 100,000 at its peak. The city is noted for its architectural complexity, with structures like the Pyramids of the Sun and the Moon and the Temple of the Feathered Serpent all connected amongst numerous residences by the Avenue of the Dead.

It was beneath the Temple of the Feathered Serpent that a sealed-off passage was discovered in 2015, which led to a tunnel deep beneath the ground. When 21st-century archeologists dared to venture down into it, they could not, in their wildest dreams, have imagined what they would find.

Mexican archeologist Sergio Gomez Chavez led the subterranean expedition after chancing upon the tunnel himself. He later recalled the potent stench of the tunnels upon unsealing them. The smell was almost unbearable, but it confirmed that he was entering caverns that had lain undisturbed for millennia.

At first, the archeologists encountered undisturbed treasures exactly where ancient hands had placed them as divine offerings.

Amongst these eerie treasures were crystals that had been shaped into eyes, a collection of crocodile teeth, beetle wings which had been meticulously arranged in a box, hundreds of small metal spheres, and intricate sculptures of jaguars poised to pounce on any who might dare to disturb the ancient tunnel.

They found the most stunning feature fifty-six feet beneath the surface – a model of the region's mountainous landscape. The walls around this section of the tunnel had been painstakingly decorated with fool's gold and reflective stones so that, in the firelight, it would sparkle like a galaxy of stars.

A nearby rubber ball, once used for ancient sports games, represented the sun. However, most fascinatingly, between these miniature mountains were found lakes of liquid mercury -- molten, shimmering pools which had remained in their place since Biblical times.

One theory proposes that the pools were part of an elaborate representation of the underworld -- a realm of dark creation where souls are reborn. In this interpretation, the reflective quality of the mercury would have mimicked the sheen of watery realms associated with the afterlife in Mesoamerican mythology.

Mercury is a naturally occurring element, yet its presence in ancient contexts is unusual due to its rarity and toxicity. Control over mercury — a rare and precious substance — would have reflected and reinforced the status of Teotihuacan's elite.

The name 'Teotihuacan' translates to ‘the place where gods were created.' Standing above the tunnel's miniature underworld, where shimmering lakes of mercury meet a sparkling galaxy of pyrite overhead, one can easily imagine how its creators must have felt like gods themselves...