Theodosian Walls of Constantinople

A siege the Byzantines had survived twenty-three times

Constantinople had withstood twenty-three previous sieges in the eleven centuries since its founding by Constantine in AD 330. By Avars, Slavs, Arabs, Bulgars, Russians, and various Latin Crusader factions.

The triple-line Theodosian Walls, built around AD 408, were the most formidable urban fortification in the medieval world. They had never been breached by direct assault.

The defenders in 1453 numbered roughly 7 000. The besieging Ottoman army was perhaps 80 000. By the medieval standards of siege warfare, the walls should have held.

A Hungarian named Orban

What changed was a Hungarian (or possibly Transylvanian) cannon founder named Orban, who in 1452 offered his services first to the Byzantine emperor Constantine XI Palaiologos.

Constantine could not afford the price. Orban took his designs to Sultan Mehmed II instead.

The result was the largest gunpowder weapon yet built: a bronze bombard 8.2 metres long, weighing 17 tonnes, firing stone balls of 270 kilograms — not 540 kilograms as some modern sources repeat. Orban built a dozen smaller bombards in support. The siege guns required 60 oxen and 200 men to drag from Edirne to Constantinople, but once in place they could fire seven times a day at the same section of wall.

Ships over a mountain

Constantinople's Golden Horn harbour was protected by a chain boom strung across its entrance — a heavy iron chain anchored on both sides that prevented enemy ships from entering. The Ottoman navy had no way through.

Mehmed II's solution was to portage 80 ships overland.

Greased wooden tracks were laid up a hill north of the city. The ships were dragged up by ox-teams and rolled down the other side directly into the Golden Horn behind the chain. The whole operation took a single night of 22 April 1453.

With the Ottoman fleet now inside the Golden Horn the defenders had to divide their forces, weakening the land walls just as the bombardment was beginning to tell.

The final assault, and the missing emperor

The decisive Ottoman assault began at 1 a.m. on 29 May 1453.

The breach at the Gate of St. Romanos had been widened over the preceding days. The Ottoman attack rolled in three waves — irregulars first, then Anatolian troops, finally the elite Janissaries.

Giustiniani Longo, the Genoese mercenary commanding the defence at the breach, was wounded around 2 a.m. and was carried away. The Genoese took this as a withdrawal signal and abandoned their post. Within an hour the breach was held by Janissaries, and the city was lost.

Emperor Constantine XI removed his imperial insignia and died fighting on foot in the breach, sword in hand. His body was never identified. A persistent Greek legend says he was turned into marble and hidden in a cave by an angel, to return at the moment Constantinople is liberated.

The city has been called Istanbul for 572 years.