© Gizmodo
Teotihuacan, an ancient, abandoned city about an hour north of Mexico City, was once one of the largest cities in the world. It collapsed in the centuries ago (thanks either to an internal uprising or foreign invaders, depending on who you ask), but it's never been completely deserted, since the ruins have always been a magnet for squatters, archaeologists and hordes of tourists.

Yet there are still portions of Teotihuacan that remain untouched by today's explorers, including a subterranean burial site that scientists estimate has spent the last 1900 years unseen by human eyes. Until now.

© Gizmodo
In 2003, scientists discovered a tunnel beneath Teotihuacan's Temple of the Plumed Serpent. They speculated that the tunnel was a processional walkway leading to a warren of royal burial chambers, but couldn't say for sure, since the opening to the tunnel was intentionally buried by the city's last inhabitants. According to BLDGBLOG, archaeologists at Mexico's National Anthropology and History Institute are now uncovering the mystery of the buried chambers without disturbing them - thanks to a diminutive robotic system designed to go where shimmying archaeologists cannot:
... A little wireless robot called Tlaloc II-TC will soon "investigate the far reaches of a tunnel found beneath the Temple of the Plumed Serpent at Teotihuacan," entering a chamber "estimated to be 2,000 years old, and [that] may have been used as a place for royal ceremonies or burials."
Tlaloc Enters Tunnel
© Alma Rodríguez for El UniversalThe first Tlaloc enters the tunnel..
Tlaloque is actually a deployable collection of three different robotic systems. The largest, a Mars Rover-esque contraption, is in charge of transporting two smaller mechanisms through the rubble-filled tunnel. When it reaches the chambers, a second vehicle is programmed to unpack itself to take infrared scans of the space. Finally, a smaller, winged contraption will eventually be deployed to capture video footage. BLDGBLOG explains:
It gets even more interesting when we then read that there is yet another, "third part" of the ensemble, a "robot made with four propellers" that can "remain suspended in the air and take pictures with video cameras."

It's a drone, in other words - part of a whole family of proliferating machines - but, for now, it will only be "used outdoors due to currents of air in the tunnel."
Tlaloc II
© Melitón Tapia/INAHTlaloc II-TC, the latest iteration of the system.
The team at the INAH have tested several iterations of Tlaloque, so there are a few preliminary reports of what's actually inside the chambers - and it sounds amazingly spooky and cool. "Investigations [have verified] that the tunnel was constructed before the Feathered Serpent Temple and the Citadel, structures that were the scenario of rituals linked to original creation myths," reported scientists in 2010. "[Meanwhile] the tunnel must have been related to the underworld concept." According to a report in Provincia, images show a series of stone symbols lining the tunnel, which scientists believe was "subsequently collapsed in order to deposit something very important at the end the duct in the main chamber."

Transmitted Image
© INAHTlaloc I’s first transmitted image.
This isn't the first instance of "drone archaeology". In 2011, scientists in East-Central Asia used a microdrone to generate an aerial map of Scythian burial grounds in the remote Altai Mountains. And in Peru last year, archaeologists used an unmanned aerial vehicle to survey the abandoned city of Mawchu Lllacta. Still, it's remarkable to watch how archaeological discovery is evolving alongside drone technology.

As for what's to come from beneath the temple at Teotihuacan, Provincia reports that the aerial drone is currently under testing. That means we'll likely get to see video of the chamber before long - and suddenly, a site that's been closed to humans for nearly two millennia will be revealed to an audience of millions.