1,600-Year-Old Tunnel Network Beneath Hagia Sophia as About 3,000 Tons of Debris Are Cleared

Archaeologists have removed roughly 3,000 tons of debris from a centuries-old network of underground tunnels beneath Istanbul's Hagia Sophia, revealing sections that were previously inaccessible beneath one of the world's most historic religious landmarks.

The findings were announced by archaeologist Hasan Fırat Diker at a presentation this fall in Istanbul, on October 16, as the local outlet Türkiye Today reported. The tunnels have been undergoing excavation and clearing work since February 2025, allowing researchers to explore sections previously buried beneath mud and debris.

According to Diker's research, the roughly 1,600-year-old tunnels were built by the Romans and originally functioned as part of the city's water distribution and drainage network, while also providing a protected underground space.

Some of the underground structures predate the present-day Hagia Sophia, which was completed in 537 A.D. under Byzantine Emperor Justinian I. Diker said the landmark is actually the third structure built at the site.

Although the underground network has been known for decades, much of it has remained difficult to access. Türkiye Today said Diker compared the intricate network to a modern subway system. The tunnels were designed to carry rainwater from surrounding streets into the sea, according to Diker.

Researchers have cleared nearly 558 feet of an underground route connected to a fifth-century Roman street, which extends from the Sarayburnu area toward Little Hagia Sophia, Diker said.

Diker said his team had cleared both the upper and lower sections of an ancient underground burial complex discovered in 1946, excavating an additional five feet beneath it. The burial chambers predate the current Hagia Sophia and had accumulated large amounts of mud over the centuries, according to Diker.

Hagia Sophia means “Holy Wisdom” in Greek. It served as a major center of Eastern Christianity for nearly 1,000 years until Ottoman forces conquered then-Constantinople and converted the church into a mosque in 1453. It later became a museum in 1935 before being converted back into a mosque in 2020. The landmark, part of a UNESCO World Heritage Site, is visited by millions of tourists each year. Looking ahead, Diker said researchers hope to open more sections of the underground network to visitors, with plans for an exhibition showcasing the archaeological discoveries.