The Day the Middle Ages Ended 

By 1453 the Roman Empire was a city and not much else. The territory that once ran from Britain to the Euphrates had shrunk to Constantinople, a slice of Greece and a few islands, with perhaps fifty thousand people rattling around inside walls built for half a million.

What kept it alive was the Theodosian land walls: a triple line of ditch, outer wall and inner wall, raised in the fifth century and never taken by direct assault in a thousand years of trying. Fortification like that made the city a strategic problem that armies simply went around.

Then the arithmetic changed. Mehmed II came to the throne at nineteen and commissioned artillery on a scale nobody had built, including a bombard reportedly over eight metres long, cast by a Hungarian engineer named Orban who had offered his services to the emperor first and been turned down for lack of money. Stone walls designed against battering rams and ladders had no answer to sustained gunpowder bombardment.

The siege ran from 6 April to 29 May 1453. Defenders under Constantine XI and the Genoese commander Giovanni Giustiniani numbered perhaps seven thousand against an Ottoman force many times that. The chain across the Golden Horn was outflanked by hauling ships overland on greased rollers. When the walls finally broke near the Kerkoporta, an empire that had counted its emperors since Augustus ended in a single morning, and Greek scholars carrying manuscripts began arriving in Italy.