Researchers Have Found an Inca Tunnel Beneath the Peruvian City of Cusco

It’s long been rumored that a network of old, underground tunnels lies beneath Cusco, Peru, the capital of the ancient Incan empire. Now, thanks to archival texts and ground-penetrating radar, researchers say they’ve confirmed the tunnels’ existence.

Archaeologists Jorge Calero Flores and Mildred Fernández Palomino, leaders of the research project, recently announced their findings at a press conference, according to a translated Facebook post by the Association of Archaeologists of Peru. Flores said the team found an underground passage connecting two of Cusco’s key Inca monuments: the Temple of the Sun—which conquistadors ruined and covered with a Catholic church in the 16th century—and the Sacsayhuamán fortress, a 15th-century Inca monument of stone walls more than a mile away.

The Inca dominated Peru’s Andes Mountains and jungles for centuries. They established their capital of Cusco in the 12th century, then conquered swaths of land between the early 15th and 16th centuries, after which the empire controlled some 12 million people. It was during this century of expansion that the Inca built Machu Picchu, the famed “lost city” perched on a mountaintop 50 miles from Cusco. In the mid- to late-16th century, the Inca empire—weakened by internal strife—fell to the rule of invading Spanish colonizers.

The Inca left no written records of their underground constructions in Cusco, but Spaniards did. A 1594 text by an anonymous Spanish Jesuit describes a tunnel that begins at the Temple of the Sun, runs beneath the bishop housing behind Cusco Cathedral and ends at Sacsayhuamán, reports IFL Science’s Benjamin Taub. Another text, written by Jesuit chronicler Juan Anello de Oliva, alludes to several tunnels beneath Cusco—accessible from a cave in the Sacsayhuamán fortress—and says construction workers took care to avoid the tunnels during work, per Popular Mechanics’ Tim Newcomb. As Flores said at the press conference, these records gave his team an idea of where to look.

At the sites, researchers used acoustic prospecting—directed sound waves—to discover hollow areas underground. They then employed ground-penetrating radar to make a map of the tunnel. According to the Association of Archaeologists of Peru, the team identified a mile-long stretch of tunnel between the fortress and temple.

Flores said the passage is about 8.5 feet wide and just over 5 feet tall, per El País’ Renzo Gomez Vega. Inca builders constructed the so-called Chincana by digging a ditch, lining it with stone walls and covering it with beams and ceiling. According to IFL Science, researchers say these dug-out passages probably ran directly under Cusco’s aboveground streets and walkways.

The Chincana’s purpose remains a mystery. Palomino said the research team plans to explore the tunnels themselves to learn more about them. Per IFL Science, she told reporters, “Now we have to excavate at key points to be able to enter the Chincana—perhaps in March or April.”