What is the name of the natural harbor of Constantinople?

The natural harbor of Constantinople was the Golden Horn. Known in Turkish as the Haliç, it is a horn-shaped inlet and estuary where the Bosporus meets the Sea of Marmara. Its sheltered waters formed the northern boundary of Constantinople’s historic peninsula and gave the city an exceptionally valuable maritime position.

The harbor supported trade, naval activity, and the movement of supplies throughout Byzantine and later Ottoman history. Its protection from severe winds and waves made it safer than the more exposed shores of the Marmara. Constantinople’s sea walls and harbor defenses, including the famous chain stretched across its entrance, helped protect the city from attack.

A common mix-up is confusing the Golden Horn with the Bosporus. The Bosporus is the strait connecting the Black Sea and the Sea of Marmara; the Golden Horn is an inlet branching from it. The Dardanelles, farther west, connects the Aegean Sea with the Sea of Marmara.