The siege proper began on 6 April when the Sultan’s cannon started their bombardment of the city’s defences after the Emperor had turned down the obligatory Islamic offer to spare the lives of the inhabitants if they surrendered. The Turkish artillery included a massive cannon cast on Mehmet’s specific orders. It was designed for him by an itinerant engineer named Urban who was appointed by the Sultan in 1452. He may have been either German or Hungarian and was an expert armourer.
Urban had previously approached the Emperor with an offer to design and build cannon for the Empire. However, Constantine had to send him away; the Empire was by that time too poor to employ him and could not obtain the required raw materials. We know history turns on many small events, in this case a recruiting decision? How different might it have been had Urban offered his services elsewhere in Europe. The Empire was in terminal decline at this stage and the outcome was almost inevitable. If the Fall had not been in 1453 it would most likely have occurred in the next few years.
So what was special about Urban’s cannon? He had already built one large cannon for the Sultan which was placed at his newly constructed fortress of Boghaz Kesen, meaning “the cutter of the Strait” or “of the Throat” (referring to the narrowest point of the Bosphorus). The Byzantines called this Rumeli Hisar, or “The castle of Romeland”, which was a pretty good name as it was the medieval equivalent of the Sultan parking his tank on the Emperor’s lawn. Mehmet could do as he pleased and respected no treaties. The fortress cannon was used to enforce the Sultan’s new tax on every ship that passed through the straits. On one occasion a Venetian ship tried to run this blockade and was sunk.
The new cannon (and we don’t appear to have a name for this – typically one-off, unwieldy, but morale crushing weapons have names like “Deliverer of Death” or even “Supergun” but nothing appears to survive) was apparently nearly twenty-eight feet long, its barrel was two and a half feet in diameter at the business end, and the bronze was at least eight inches thick. During field tests (when the local inhabitants were warned not to be alarmed about the noise!) it fired a cannon ball weighing 1,340 pounds well over a mile before it buried itself six feet in the ground. The noise could be heard over ten miles.
The monster cannon had seven hundred men to service and support it (you can bet they gave it a name); and fifteen pairs of oxen to haul it. Roads and bridges had to be strengthened along the route from the Sultan’s foundry in Adrianople. Such a combined artillery force had never before been seen in the East, although it had been fairly common in Western Europe for the last one hundred years.
The bombardment that day was unprecedented. By the end of the first day a section of the wall near the Charisius Gate was reduced to rubble and Turkish soldiers attempted to storm the walls. Despite repeated charges they were driven back, and night fell bringing a degree of peace. However, a pattern now emerged. Over the coming weeks the Turks would create breaches by day only for the defenders to rebuild the walls and towers overnight, sometimes using brick and stone, at other times using wooden stockades and earth filled barrels. With his 100,000 men the Sultan could rest his men and attack in relays. The defenders had no such opportunity fighting by day, patrolling and rebuilding by night, they must have reached a state of exhaustion. But they had survived the first day, and it was the Sultan who had suffered more casualties and had to rethink his plans. This he did, and displayed genuine tactical agility and improvisation as we shall see in the coming weeks.