The Gül (Rose) Mosque stands as a compelling architectural building in the historic Ayakapı district, marking the profound transition of Istanbul from the Byzantine era to the Ottoman period. In the 8th century, Constantinople was gripped by Iconoclasm, a movement where authorities banned and destroyed all religious images of Jesus and the saints. Amid this turmoil, a woman named Theodosia made a final stand. When soldiers arrived at the Chalke Gate to tear down a revered image of Christ, she courageously intervened. She viewed this not as a political protest, but as a sacred defense of her faith. For her defiance, she was martyred.  When the era of destruction ended, the city honored her memory by dedicating a church in her name: Hagia Theodosia. Despite popular legends claiming the building was decorated with roses on the day of the 1453 conquest, the name "Rose" most likely originates from a dervish tomb inside or other forgotten traditions of the site. Serving initially as a Byzantine shrine and later as a naval warehouse, the structure was thoughtfully converted into a mosque, preserving the rich historical layers of the Byzantine era. The building serves as a masterclass in architectural adaptation, showcasing a classic Byzantine "cross-in-square" plan that was later refined by Ottoman architects. Visitors can easily distinguish these two eras by observing the structure. The massive stone piers and the core cross-shaped layout are remnants of the original church, while the pointed arches, side windows, and stepped rooflines reflect the Turkish classical style implemented after the 1509 earthquake. Unlike the intricate mosaics found in other Byzantine churches, the interior today features elegant 19th-century hand-painted patterns. It remains a rare, physical testament to how two distinct empires left their enduring marks on the same stone walls. Today, it is one of the preserved mosques, a layer multi faith past of Istanbul.