A restoration campaign at Istanbul’s Hagia Sophia has revealed seven underground tunnel lines thought to be around 1,600 years old, adding a tangible new layer to long-running stories about what lies beneath the famed monument. The tunnels were documented during cleaning and survey work in garden areas around the structure, alongside a hypogeum (an underground burial complex). The find comes as officials stress that the wider conservation program is being run under scientific oversight, with the building’s long-term safety a central aim reports Türkiye Today.
A Hidden Network from the Early Byzantine Era
Turkey’s Culture and Tourism Minister Mehmet Nuri Ersoy said the tunnel work forms part of a larger, multi-stage restoration that includes scanning, modelling and careful material analysis across the site. In remarks reported by Anadolu Agency and republished by NTV, Ersoy also pointed to the scale of underground clearing: “we documented seven tunnel lines… and removed 1,068 tons of soil fill” during cleaning operations, while a separate underground burial area saw another 102 tons removed. The same report describes multiple underground “spaces” and linked tunnels in the western garden and northern (Vezir) garden areas.
A view of two of the underground tunnels discovered beneath Hagia Sophia, Istanbul, Turkey. (Photo via Ministry of Culture and Tourism)
This isn’t the first time Hagia Sophia’s subterranean story has surfaced, but the latest documentation is unusually concrete: named tunnel “lines,” measured spoil removed, and on-site visual records presented publicly. Prof. Hasan Fırat Diker, who has worked on mapping and understanding the monument’s below-ground infrastructure, has previously described tunnel and culvert systems around the building as crucial to ventilation and water management, not romantic “escape routes.” Those practical functions help explain why so much of the underground fabric sits close to the structure’s foundations and gardens rather than forming a single, straight passage.
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A view inside one of the underground tunnels discovered beneath Hagia Sophia, Istanbul, Turkey. (Photo via Ministry of Culture and Tourism)
Why Restoration is Turning Underground Now
Restoration updates suggest the underground work is not happening in isolation, but alongside major efforts above ground—scaffolding, façade cleaning, and structural checks intended to preserve the building for centuries. In the same Anadolu Agency coverage carried by NTV, Ersoy emphasized process as much as progress, saying: “we don’t do any work without scientific assessments and without meeting contemporary restoration requirements.” That matters at Hagia Sophia, where earlier interventions introduced materials such as cement-based plasters that specialists now consider inappropriate for historic stone and brick.
The timing also reflects a broader concern: Istanbul’s earthquake risk, and the need to understand not just what visitors see, but what the monument stands on. Anadolu Agency has reported that Hagia Sophia’s long life includes dome collapses and major repairs after earthquakes, with modern engineers focusing on vulnerable structural points while trying not to “alienate” the building through heavy-handed intervention. Even when the work is visible (platforms, scaffolding, roof projects) its logic is often subterranean: load paths, drainage, humidity control and the health of the foundations.
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Scaffolding on the dome of Hagia Sophia during restoration work. (David Bjorgen/BY-SA 2.5)
The Deeper Context: a City Built with Water Below Its Feet
Hagia Sophia’s “underground” is also part of a much larger Istanbul reality: a historic city shaped by cisterns, conduits and storage systems that once kept palaces, churches and neighbourhoods supplied. The present Hagia Sophia was built in 532–537 AD under Emperor Justinian I, after earlier churches on the site were damaged or destroyed, and that it has repeatedly been repaired following earthquakes - an architectural life story that makes hidden infrastructure more than a curiosity. In other words, what is being cleared now may be as essential to survival as the dome above.
Just a short walk away, the Basilica Cistern offers a public example of how Byzantine Istanbul managed water on a vast scale - one reason tunnel-like maintenance spaces around major monuments are so plausible. Ancient Origins has previously explored the relationship between Hagia Sophia and nearby water systems, including the Basilica Cistern and wells identified in surveys around the monument. The newly documented tunnel lines may ultimately help researchers understand how drainage, humidity and maintenance were handled in different phases - Byzantine, Middle Byzantine and Ottoman - without relying on myths alone.
Top image: The Basilica Cistern, part of Istanbul’s famous underground water landscape near Hagia Sophia. Source: Taco325i/CC BY-SA 3.0
By Gary Manners
References
Anadolu Ajansı. 27 February 2026. Ayasofya'da restorasyon sürüyor: “Her işlem bilimsel yöntemler ışığında yapılıyor”. Available at: https://www.ntv.com.tr/galeri/turkiye/ayasofyada-restorasyon-suruyor-her-islem-bilimsel-yontemler-isiginda-yapiliyor-1713812
Bayar, G. n.d. Anadolu Agency team enters largest underground structures of Hagia Sophia. Available at: https://www.aa.com.tr/en/culture/anadolu-agency-team-enters-largest-underground-structures-of-hagia-sophia/2671672
Encyclopaedia Britannica. n.d. Hagia Sophia. Available at: https://www.britannica.com/topic/Hagia-Sophia
Türkiye Today. 27 February 2026. 1600-year-old underground tunnels discovered under Hagia Sophia during restoration. Available at: https://www.turkiyetoday.com/culture/1600-year-old-underground-tunnels-discovered-under-hagia-sophia-during-restoration-3215271
