I saw in a documentary that, allegedly, castles were only built with round towers after the advent of cannon. The basis for this statement was that cannonballs, etc would more easily glance off a round wall rather than a square corner. This makes sense, and from what I’ve been able to find from basic cursory searches, most sources say round castle towers were a much better defense against siege weaponry in general. And the older castles that still stand today seem to mainly feature rectangular or polygonal towers.
That said, when do the first castles with round towers appear? Of course there are not many surviving castles today from before the 14th century (that haven’t been heavily modified since then). But is there any archaeological evidence or otherwise that shows any castles with round towers before that point? If purely mechanical siege weapons were already a threat long before gunpowder, wouldn’t it make sense for round towers to precede cannon? Lastly, did brochs or Irish round towers ever have any influence on castle architecture?
Thanks in advance!
No, that is not true, and I can't fathom how someone would come to that conclusion. Round towers were used from at least the mid 12th century, when Krak des Chevaliers was built. By the 13th century, most castles were being built with round towers. Edward I's Welsh castles, most of which survive, have round towers. Where they came from originally, I can't say. They may have been brought back from the Levant, or they may have developed independently in Europe.
The response to the increasing effectiveness of cannon (and this doesn't occur until the early 16th century, during the French wars in Italy) was to not build towers at all. Military engineering underwent a genuine revolution. Walls were now built lower, much thicker, and studded with various works (bastions, flankers, lunettes, etc) that projected out from the wall to ensure any attackers would be enfiladed even if they hugged the walls. A combination of glacis (sloped earthen ramps to deflect cannon shots upward), trenches, and outer works provided protection to the walls themselves.
This could be in Simple Questions . Stone is extremely strong in compression ( hard to squeeze a rock) and the weight of the stones really gives a masonry stone wall much of its strength. However, a masonry stone wall has little tensile strength: it's not too hard to crack a stone apart, and it is pretty easy to pull apart stones held together by mortar- especially the old style mortar which was mostly lime. Any siege army could send a team with prybars and hammers to knock at the corner of square tower, and if they weren't stopped they could soon create a notch. A stone tower with a big notch in the corner could fall. Take away the corners - make the towers round- and making a notch was much harder to do.
In cities with older brick and stone buildings, you will still find small round buttresses on their corners to keep horse-drawn wagons and carriages from damaging them.