In the ancient city of Teotihuacán, northeast of Mexico City, archaeologists have discovered a secret tunnel. For centuries, the tunnel has remained hidden beneath the famous and massive Pyramid of the Moon.

Pyramid of the Moon
The Pyramid of the Moon is the second-largest structure in the ancient city. The largest is the Pyramid of the Sun, according to the International Business Times. The archaeologists who discovered it believe that the tunnel mirrors the Teotihuacáns' great monuments. It may represent the underworld in the belief system of the 2,000-year-old civilization that existed before the arrival of Christopher Columbus. The Teotihuacán civilization is also thought to predate the Aztecs, who later inhabited the site.

The tunnel extends from the central square known as the Plaza de la Luna to the Pyramid of the Moon. It is about 10 meters (33 feet) deep. The underground passage is similar to other tunnels that have been discovered recently, like the tunnel that was found under the Temple of the Plumed Serpent.

No one has been able to go inside the tunnel yet. The discovery was made through a method known as electrical resistivity tomography. This method creates images of Earth's landscape below the surface. A team of archaeologists from Mexico's National Institute of Anthropology and History was using the method as part of their conservation efforts for the central square when they stumbled upon the tunnel.

Pyramid Had Been Used for Ritual Sacrifice
The Pyramid of the Moon was likely used for human sacrifice and other religious ceremonies due to human remains found at burial sites. It is unclear what the tunnel may have been used for. Archaeologists plan to do more research to determine its purpose and whether or not it contains more artifacts.

Teotihuacán was a major city for a long time and had a complex history, much of which has yet to be unwound. It was one of the largest cities in the Americas in the era before Columbus and has been home to at least 125,000 people.