Pyramid of the Moon: Secret Tunnel and Chamber Discovered in Teotihuacán City Could Be Passage to Underworld

View of the 'Pyramid of the Moon' at the archaeological site of Teotihuacan, 28 January 2008. Archaeologists have discovered a tunnel beneath the ancient structure. Ronaldo Schemidt/AFP/Getty Images

Archeologists have found a tunnel and a chamber beneath the Pyramid of the Moon in Mexico, which is thought to have been used in rituals related to what ancient people thought was the underworld.

The chamber measuring 15-meters in diameter, as well as a tunnel running to the south of the Plaza de la Luna in the city of Teotihuacan, was discovered 8 meters beneath Mexico's second largest pyramid, according to a statement by the National Institute of Anthropology and History.

Experts who carried out the work believe objects such as skulls and jewelery could also be awaiting discovery, as well as an entrance to the tunnel on the east side of the pyramid.

Researchers have been investigating the site of the Pyramid of the Moon since the 17th century. In the 1980s archeologists Rubén Cabrera and Saburo Sugiyama found skeletons of individuals with cranial deformations as well objects made of green stone, necklaces, and anthropomorphic figurines in tunnels excavated under the pyramid.

"So it is not difficult to think that something similar could be found in the subsoil," Ortega said.

A religious and economic hub at around 500 CE, the city of Teotihuacán, or City of the Gods in Nahuatl (a language spoken by the Aztecs), sits around 30 miles northeast of Mexico City.

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Up to 200,000 people were believed to live in Teotihuacán at its height making it one of world's most populous cities at the time.

It is also the location of the Pyramid of the Sun, the biggest pyramid in Mexico and the largest of such monuments in the Western Hemisphere. In 1987, the UN named Teotihuacán a UNESCO World Heritage site.

Dr. Verónica Ortega, director of the Integral Conservation Project of the Plaza de la Luna, said in a statement that the room in the structure known as Meztli Itzácual by the ancient city's inhabitants could have been used for rituals by the Toltec peoples.

The researchers did not set out to find a burial chamber, said Ortega, but to investigate the space that worshippers probably believed was linked to the "underworld" and which was thought to give the city sacred properties.

A team of experts from National Institute of Anthropology and History (INAH)and the Institute of Geophysics Institute of the National Autonomous University of Mexico made the findings after carrying out tests on the monument in June 2017.

The passage and chamber could offer insight into the influence and importance of the ancient metropolis in relation to other parts of Mesoamerica.

Towering at 140 feet (43 meters) high with a base measuring 426 by 511 feet (130 by 156 meters), the Pyramid of the Moon faces the northern end of Teotihuacan's Calzada de los Muertos, or Avenue of the Dead. Little is known about the Pyramid of the Moon as well as the nearby Pyramid of the Sun, as few excavations have taken place at the sites, Ortega explained.