Perched on the Anatolian side of the Bosphorus, near its Black Sea entrance, Beykoz Castle, commonly known as Yoros Castle, was strategically built to control maritime passage, along with its counterpart, İmros Castle on the Rumeli side. Though often attributed to the Genoese, inscriptions in Greek letters on its towers confirm its Byzantine origins. The name Yoros is thought to derive from the Greek word "Oros" (mountain) or the ancient name "Hieron" (sacred place). The castle changed hands frequently, falling to Turkish forces in 1305 but was later taken over by the Genoese in 1348 due to their dominance over Black Sea trade routes. In the late 14th century, Ottoman Sultan Bayezid I recaptured it, using it as a military base while preparing for the conquest of Constantinople. Following Istanbul’s conquest, Sultan Bayezid II restored the fortress and added a mosque, while later expansions included a hamam and a defensive garrison. By the 16th and 17th centuries, Yoros Castle housed a small Ottoman military outpost, but its strategic importance declined over time. Today, ongoing excavations and restoration efforts, led by Istanbul University and the Ministry of Culture and Tourism, continue to uncover its Byzantine, Genoese, and Ottoman layers, making it a remarkable historical landmark with stunning views over the Bosphorus and the Black Sea.