Excavations Beneath Istanbul's Hagia Sophia Reveal Vast Underground Labyrinth
Excavations beneath Istanbul's Hagia Sophia revealed a vast, complex underground network featuring hidden passages and an enigmatic structure with an unknown purpose.
Extensive cleaning and restoration work carried out beneath the Hagia Sophia in Istanbul has revealed an underground network far more complex and vast than previously known to science. According to a new study published in the journal Open Archaeology and led by Prof. Hasan Firat Diker, the removal of some 300 tons of earth and debris from the depths of the Byzantine site has uncovered a long series of previously undocumented passages, channels, and hidden structures.
While a significant portion of the infrastructure was used for managing and transporting water in the historic city, the researchers' main focus is an anomalous and mysterious structure whose purpose remains a riddle. The Hagia Sophia itself, constructed between 532 and 537 CE during the reign of the Byzantine Emperor Justinian I, conceals a complex history rooted in even earlier phases.
Mapping the Hidden Labyrinth
The full extent of the tunnel system only began to emerge when specialized work teams descended below ground in conditions characterized by heavy darkness, narrow spaces, and poor ventilation. As part of the operation, no less than 300 tons of earth, mud, and rubble that had accumulated over centuries due to ancient collapses were cleared from the spaces.
Using advanced 3D mapping, researchers documented the findings and discovered that most spaces were indeed designed for water drainage and transport. In one area, a space containing seven parallel channels was found, indicating that the infrastructure was expanded over generations to meet the needs of the dense urban settlement above.
The Mystery of Structure 6
Among the six main structures examined, "Structure 6" stole the show and was defined by Diker as the most enigmatic. Unlike the relatively linear paths of other tunnels, this structure features an irregular geometric layout, numerous branches, and an open-frame design.
The biggest surprise was discovered in one of the tunnel sections where eight rectangular niches were exposed, recessed into the walls beneath unique masonry vaults. Unlike the rest of the underground network, no terracotta pipes were found in this area at all, completely ruling out the assumption that the place was used for water transport.
Although about 9 kilometers of tunnels have been uncovered and mapped so far, researchers estimate that the work is far from complete, as vast sections of the passages remain completely blocked.
