Ottomans attacked Constantinople constantly, but could not get the results because European countries sent reinforcements constantly. In May, a lot of Ottoman soldiers died. The Byzantine empire defended successfully. Ottomans wanted to enter Golden Horn. Because, the Byzantine walls were too weak there. But, there was a thick chain in entry of Golden Horn so, Ottomans ships could not enter Golden Horn. Mehmed II ordered about this problem. Ottomans ships passed on the Kasımpaşa. Thus, Ottomans entered Golden Horn! This order was incredible! And a lot of Ottoman ships passed on Kasımpaşa (which is the shore of Golden Horn) by pulling all ships over Kasımpaşa by ropes by Ottoman's soldiers . Ottoman ships entered Golden Horn and attacked Byzantine ships. A lot of Byzantine ships sunk. Constantinople became too weak, after this attack. Thus, few days later, Ottomans captured Constantinople and Byzantine empire fell. Mehmed II made it capital city of Ottoman empire. New mosques, hospitals, schools, buildings and a university (Istanbul University) were founded here.