Byzantion was founded by Greek colonists from Megara in 657 B.C. In 340 B.C., the Byzantines, with the aid of the Athenians, successfully withstood a siege by Philip of Macedon. They were, however, forced to recognize Macedonian suzerainty after surrendering without a fight to Alexander the Great in 334 B.C. The city was rebuilt as the new capital of the Roman Empire by Constantine I in 330 A.D. and renamed Constantinople. It became the capital of the Ottoman Empire when it was conquered in 1453. Today it is Istanbul, the largest city in Turkey, and the country's economic, cultural, and historical heart.