Constantine the Eleventh Palaiologos, the last emperor of Rome, stood inside the Hagia Sophia on the night of 28 May 1453. Candles burned around a congregation that knew it might not see morning. Prayers rose in both Greek and Latin for the first time, two churches briefly united by terror.

The city Constantine defended was already a ghost of empire. The Black Death had killed nearly half its population a century before. By 1453, Constantinople was a patchwork of walled villages separated by open fields, defended by fewer than eight thousand men against an Ottoman army of fifty thousand or more.

That army belonged to Mehmed the Second, an Ottoman sultan who had taken the throne at nineteen. European courts had dismissed him as inexperienced. He answered them by building a fortress across the Bosphorus to strangle the city's sea lanes, then dragging an artillery train hundreds of miles from his capital at Edirne, including a twenty-seven-foot cannon built by a Hungarian engineer named Orban, capable of hurling a stone ball over a mile.

The fifty-three-day siege began on 6 April 1453. Ottoman cannons hammered the ancient Theodosian walls daily. The defenders patched the gaps each night. When the chain across the Golden Horn blocked his fleet, Mehmed had his ships hauled overland on greased logs and floated them inside the harbour, threatening the city from a new direction. Constantine sent word to the West; no fleet came.

On 21 May, Mehmed offered terms: surrender the city and the Emperor could rule the Peloponnese in peace. Constantine refused. He would die in Constantinople, he said, of his own free will.

Shortly after midnight on Tuesday 29 May, the final assault began. Wave after wave struck the land walls. The Genoese commander Giovanni Giustiniani, who had led the defence of the ramparts, was gravely wounded and carried from the walls. His retreat broke the defenders' nerve. The Janissaries poured through.

Constantine tore off his imperial regalia and led a last charge into the streets. He was never seen alive again. His fate remains uncertain, but he did not surrender and he did not escape. The Roman Empire, which had begun under Augustus roughly fifteen hundred years before, ended somewhere in the rubble of those streets.

Mehmed rode into the city and entered the Hagia Sophia, marvelling at the great dome above him. He ordered a muezzin to the pulpit. The church was converted into a mosque that same day. Around thirty thousand of the city's surviving inhabitants were enslaved. The sultan renamed himself Kayser-i Rum, Caesar of the Romans, and made Constantinople his capital.

The fall sent Greek scholars westward with manuscripts and learning that helped fuel the Renaissance. It ended the last trace of Rome. And it gave the Ottoman Empire the city it had sought for two centuries, a prize Mehmed's own soldiers called the greatest of conquests.