The Ottoman capture of Constantinople on May 29, 1453, by Sultan Mehmed II — the conquest that ended the Eastern Roman, or Byzantine, Empire after more than a thousand years centered on Constantinople, made the city the seat of a new Islamic empire, and was read across Christian Europe as the close of one age and the start of another.
A twenty-one-year-old sultan stood before walls that had turned away armies for a thousand years. The triple land walls of Constantinople were the most famous fortifications in the world, and they had never been breached by direct assault, even though the city itself had once fallen from the sea two centuries earlier. Mehmed II did not plan to rely on assault alone. He had something the old walls were never built to face: cannon large enough to crack stone that had held since the age of the Caesars. When the walls finally broke, the line of Roman emperors that ran back past Augustus broke with them.