53 days of cannon fire 

The siege began on 6 April 1453 and ended on 29 May, fifty-three days later. Almost all of that time was bombardment, and it is the least cinematic and most instructive part of the story.

Mehmed's artillery train included many guns of ordinary size and a small number of enormous ones, and the enormous ones were slow. A great bombard had to be laid, wedged, loaded, fired, then left to cool before the barrel could safely take another charge, so it managed only a handful of shots in a day. Aim was crude in the sense that no gunner could place a ball precisely, but perfectly adequate in the sense that a wall six kilometres long is a large target. The method was to pound one section repeatedly, working a triangular pattern of hits until the masonry between them collapsed.

Against this the defenders had a technique that is almost domestic. Each night, under torchlight, soldiers and civilians including women and monks carried rubble, earth, timber and brushwood into the gaps. They filled breaches with a rammed mixture of stone and soil, faced with bundles of vine-stakes and barrels of earth, and by morning there was a new obstacle in place. It was not stone and it did not look impressive, but earth and fascine absorb cannon shot far better than rigid masonry does, which is why the fortification engineers of the following century abandoned high stone walls in favour of low earthen bastions.

For weeks this improvisation worked. The Ottomans also mined, and the defenders countermined and flooded or fired the tunnels. They repelled assaults on the makeshift barricades. But repair depends on labour, and the garrison of roughly seven thousand was doing the wall-building, the fighting and the watch-keeping with no relief and no reinforcement. A promised Venetian fleet never arrived in time. Meanwhile the damaged stretch grew longer, the rubble ran short, and the sector of the Mesoteichion, where the wall dipped into the Lycus valley and the guns were concentrated, became a permanent wound.

By late May the arithmetic was visible to everyone on both sides. Mehmed held a council, reportedly considered terms, and settled on a general assault. It went in before dawn on 29 May, in waves, at the weakest point, against defenders who had been awake for seven weeks.

What happened in the next few hours produced a legend, and the legend has a small gate at the centre of it.