Strategically set near the confluence of the Bosphorus and the Black Sea, the future site of Yoros Castle was settled by the Phoenicians and Greeks prior to the Byzantine period for trading and military purposes. The Greeks called the area Hieron (Sacred Place). The remains of temples, including Dios, Altar of the Twelve Gods, and Zeus Ourios (Zeus, granter of fair winds) were discovered in the area, dating to centuries BCE.