A secret underground passageway was uncovered during ongoing archaeological excavations in 1,500-year-old St. Polyeuktos Church in Istanbul's Saraçhane Archaeological Park, a complex that dates back to before the construction of Hagia Sophia.

A previously unknown underground passage was found about 20 meters (65 feet) from the nearby Haşim Işçan Passage. The underground passage, which contains mosaics and stone inlays, has impressed researchers with its carved marble blocks and reliefs.

Istanbul Metropolitan Municipality (IBB) Deputy Secretary-General Mahir Polat said that the structure is an excellent example of the city's architecture that has stood the test of time and the wrath of earthquakes.

Noting that the Saraçhane Archaeological Park will open for visitors in a month's time, he also said: "We have excavated the ruins of St. Polyeuktos Church, the first example of this architectural style in the world. We will continue with excavations while people are visiting. We will have the chance to explain both 'what is archaeology?' and the meaning of the historic structure. More importantly, we can explain why it's so special to be able to see a 1,500-year-old passage. Istanbul, which is currently struggling with earthquakes, has experienced dozens of earthquakes over the past 1,500 years. However, the structure we are seeing now has managed to survive all earthquakes. We should learn lessons from this."

Polat pointed out that the main structure of St. Polyeuktos was destroyed, but its infrastructure remains intact. "The earthquake memory of the city is also here. If you want to see Istanbul's earthquake memory, what happened in the Fatih district is a good example," he added.

"The mortar with a mixture known as Horasan mortar from the period. We know it is important in terms of the technology of that period. We also examined the surface samples of the structure, such as stone, plaster and possible gypsum, in the laboratory to determine their composition and archaeometry," Polat added.