Excavation Reveals Hidden Passages Beneath Istanbul’s Hagia Sophia

Archaeologists have cleared about 3,000 tons of debris from an ancient tunnel network beneath Istanbul’s Hagia Sophia, opening up passages that had been buried for centuries.

At a presentation in Istanbul on October 16, archaeologist Hasan Fırat Diker said the tunnels are roughly 1,600 years old and were built by the Romans. They served as part of the city’s water and drainage system, while also providing protected underground space.

Some of the structures beneath the site are older than the current Hagia Sophia, completed in 537 A.D. during the reign of Byzantine Emperor Justinian I. The underground network has been known about for decades, but much of it was difficult to reach. Excavation and clearing work began in February 2025.

Diker likened the complex network to a modern subway system. Its tunnels were designed to carry rainwater from nearby streets toward the sea, he said.

Researchers have cleared nearly 558 feet of a route linked to a fifth-century Roman street. The passage runs from the Sarayburnu area toward Little Hagia Sophia.

The Hagia Sophia is part of a UNESCO World Heritage Site and attracts millions of visitors each year. Diker said the landmark is the third structure to have stood at the site.

His team has also cleared the upper and lower levels of an ancient underground burial complex discovered in 1946, excavating about five feet farther beneath it. The burial chambers are older than the present-day Hagia Sophia and had filled with mud over time.

Researchers hope to open additional parts of the underground network to visitors and are planning an exhibition of archaeological remains.

Hagia Sophia, whose name means “Holy Wisdom” in Greek, was a major center of Eastern Christianity for nearly 1,000 years. After Ottoman forces captured Constantinople in 1453, the church was converted into a mosque. It became a museum in 1935 and returned to use as a mosque in 2020.

The work is part of wider archaeological interest in ancient underground passages. Earlier this year, archaeologists found a 164-foot tunnel in Jerusalem near a site associated with the biblical Kingdom of Judah. Its age and purpose are still unclear. In Germany, researchers discovered a medieval tunnel beneath a prehistoric burial site after first mistaking its entrance for a grave.