Why High-Walled Defenses Fell (literally) to Cannon
Walls
of castles and strongholds that had been built for hundreds of years
were in cross section higher than they were wider, usually by an appreciable
margin. Furthermore, they were practically vertical, which
gave them the name 'curtain walls' (see the cross-section
diagram). And their construction was unreinforced masonry (those who live in earthquake country understand the danger inherent in
this). Heavy iron balls of a few mere inches in diameter
traveling faster than the speed of sound (or near to it) had the
momentum to punch holes in these walls, thereby crack the stone and
mortar around the hit. All too soon, a weakened wall succumbed
to gravity.