Constantine XI was the last Byzantine Emperor, ruling from 1449 until his death in 1453. He was born on February 8, 1405, and became emperor during a time of great turmoil for the Byzantine Empire, which was facing threats from the expanding Ottoman Empire. Constantine XI is best known for his defense of Constantinople, the capital of the Byzantine Empire, during its siege by the Ottomans led by Sultan Mehmed II. Despite his efforts to rally support and fortify the city, Constantinople fell on May 29, 1453, marking the end of the Byzantine Empire.