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Ottoman era (1453–1922)

On 29 May 1453, the then-emergent Ottoman Empire conquered the city of Constantinople following a lengthy campaign during which the Ottomans constructed fortifications on each side of the strait, the Anadoluhisarı (Anatolian Castle, 1393) and the Rumelihisarı (European Castle, 1451), in preparation for not only the primary battle but to assert long-term control over the Bosporus and surrounding waterways. The final 53-day campaign, which resulted in Ottoman victory, constituted an important turn in world history. Together with Christopher Columbus 's first voyage to the Americas in 1492, the 1453 conquest of Constantinople is commonly noted as among the events that brought an end to the Middle Ages and marked the transition to the Renaissance and the Age of Discovery.

The event also marked the end of the Byzantines —the final remnants of the Roman Empire —and the transfer of the control of the Bosporus into Ottoman hands. The Ottomans then made Constantinople their new capital, and the base from which they expanded their empire in the centuries that followed.

At its peak between the 16th and 18th centuries, the Ottoman Empire was able to use the strategic importance of the Bosporus to wrest control of the entire Black Sea area, which they regarded as an "Ottoman lake", from which Russian warships were prohibited.

Subsequently, several international treaties have governed access to the Strait. Under the Treaty of Hünkâr İskelesi of 8 July 1833, the Bosporus and Dardanelles straits were to be closed to the naval vessels of other powers on Russian demand. By the terms of the London Straits Convention, concluded on 13 July 1841 between the Great Powers of Europe (Russia, the United Kingdom, France, Austria and Prussia), the "ancient rule" of the Ottoman Empire was re-established by closing the Turkish Straits to all warships, barring those of the Sultan 's allies during wartime. This benefited British naval power at the expense of the Russians, as the latter then lacked direct access to the Mediterranean.