The Golden Horn (Turkish: Altın Boynuz; Ancient Greek: Χρυσόκερας, Chrysókeras; Latin: Sinus Ceratinus), also known by its modern Turkish name as Haliç, is a major urban waterway and the primary inlet of the Bosphorus in Istanbul, Turkey.

This prominent body of water is a horn-shaped estuary that joins Bosphorus Strait at the immediate point where the strait meets the Sea of Marmara, thus forming a narrow, isolated peninsula, the tip of which is "Old Istanbul" (ancient Byzantium and Constantinople), and the promontory of Sarayburnu, or Seraglio Point. The Golden Horn geographically separates the historic center of Istanbul from the rest of the city, and forms a natural, sheltered harbor that has historically protected Greek, Roman, Byzantine, Ottoman and other maritime trade ships for thousands of years.

More Info: en.wikipedia.org