Istanbul (Turkish: İstanbul) is the largest city in Turkey, constituting the country's economic, cultural, and historical heart. With a population of 13.9 million, the city forms one of the largest urban agglomerations in Europe and is among the largest cities in the world by population within city limits. Istanbul's vast area of 5,343 square kilometers (2,063 sq mi) is coterminous with Istanbul Province, of which the city is the administrative capital. Istanbul is a transcontinental city, straddling the Bosphorus—one of the world's busiest waterways—in northwestern Turkey, between the Sea of Marmara and the Black Sea. Its commercial and historical center lies in Europe, while a third of its population lives in Asia.
Founded on the Sarayburnu promontory around 660 BC as Byzantium, the city now known as Istanbul developed to become one of the most significant cities in history. For nearly sixteen centuries following its reestablishment as Constantinople in 330 AD, it served as the capital of four empires: the Roman Empire (330–395), the Byzantine Empire (395–1204 and 1261–1453), the Latin Empire (1204–1261), and the Ottoman Empire (1453–1922). It was instrumental in the advancement of Christianity during Roman and Byzantine times, before the Ottomans conquered the city in 1453 and transformed it into an Islamic stronghold and the seat of the last caliphate. Although the Republic of Turkey established its capital in Ankara, palaces and imperial mosques still line Istanbul's hills as visible reminders of the city's previous central role.
The Golden Horn (Turkish: Haliç (which is derived from the Arabic word Khaleej, meaning Gulf) or Altın Boynuz (literally "Golden Horn" in Turkish); Greek: Κεράτιος Κόλπος, Keratios Kolpos: Horn-shape gulf) is an inlet of the Bosphorus dividing the city of Istanbul and forming the natural harbor that has sheltered Greek, Roman, Byzantine, Ottoman and other ships for thousands of years. It is a scimitar-shaped estuary that joins the Bosphorus just at the point where that strait enters the Sea of Marmara, thus forming a peninsula the tip of which is "Old Istanbul" (ancient Byzantion and Constantinople). Its Greek and English names mean the same, but the significance of the designation "golden" is obscure, while its Turkish name Haliç simply means "estuary". It has witnessed many tumultuous historical incidents, and its dramatic vistas have been the subject of countless works of art.