Istanbul historically known as Constantinople is the most populous city in Turkeyand the country's economic, cultural, and historical center. Istanbul is a transcontinental city in Eurasia, straddling the Bosporus Strait which separates Europe and Asia between the Sea of Marmara and the Black Sea. Istanbul for more than 2,500 years has stood between conflicting surges of religion, culture, and imperial power. A lot of nations tried to conquer the city but they failed. When the Ottomans crossed into Europe in the mid-14th century, the fate of Constantinople was sealed. The inevitable end was retarded by the defeat of the Turks at the hands of Timur in 1402; but in 1422 the Ottoman sultan of Turkey, Murad II, laid siege to Constantinople. This attempt failed, only to be repeated 30 years later. In 1453 another Ottoman sultan, Muhammad II, proceeded to blockade the Bosporus by the erection of a strong fortress at its narrowest point. The siege of the city began in April 6, 1453. The Golden Horn was protected by a chain, but the sultan succeeded in hauling his fleet by land from the Bosporus into the Golden Horn. The final assault was made on May 29, and, in spite of the desperate resistance of the inhabitants aided by the Genoese, the city fell.