The Sixteenth Century
But the Erench made much more manageable pieces and only out of bronze, which the called cannons, and used iron balls where they used to be of stone and incomparably larger and heavier; and they moved them on carts which were drawn not by oxen as was the custom in Italy, but by horses. The men and equipment assigned to this work were so skillful that they could almost always keep up with the rest of the army; and when brought up to the walls they were set up with unbelievable rapidity. With only the briefest intervals between shots, they shot so rapidly and powerfully that they could do in a few hours what in Italy used to take days.
Francesco Guicciardini, The History of Italy, trans. Cecil Grayson, ( New York, 1964), p. 153. Guicciardini was a Florentine historian of the early sixteenth century.
Just as guns profoundly changed war at sea, so they required drastic changes in siegecraft and fortification design. Guns were in use at sieges from their first appearance, but only after 1430 did they begin to have a real impact on siegecraft. It took another generation before they affected the design of fortifications.
It was in Italy that fort building first began to reflect the destructive power of artillery. The increasing use after 1470 of iron balls, which were more effective in battering the high walls and towers of medieval castles, required a reduction in their height. The lower trajectory of cannon in comparison to mechanical artillery meant that the lower part of a wall was more likely to be hit by cannonballs. That in turn meant that the rubble from a collapsed wall would probably fill the moat and make an assault on the breach easier. Lowering the walls, however, increased the likelihood of a successful escalade. The response to these problems was to make the ditch deeper and wider, so that only a small portion of the wall was raised above ground level. Machicolation atop the walls was replaced by rounded shoulders to allow balls to deflect off without doing as much damage. Gun openings, called casemates, were cut into the base of the wall to aid the defense of the ditch.