For perspective, Norman keeps were often built with a large internal cross wall, so even if troops made it through the stair door and swarmed into the room they'd still have to fight their way into the other half of the floor. By the stage these expensive and space consuming walls were defensively relevant, defenders would have already lost outer walls, viable long-term food and water supplies and much of the garrison defending it... and any real chance of holding out. But an invading army would still lose more men storming it; so it functioned as a deterrent.
I've heard this "it's a myth" argument before, but 70% of staircases is quite a large proportion of staircases spiralling in a particular direction which would offer the defender a marginal advantage to be pure coincidence. Particularly when the ratio of clockwise to anticlockwise staircases in Norman castles was about 20:1; it was later generations of castle of builders who added many more anticlockwise stairwells, in an era when individual tower defence was less importance, and builders may have simply forgotten or come to doubt arguments about the defensive advantages of clockwise spirals (the blog's arguments for why spiral staircase defence is rubbish work here of course!). Contemporary cathedrals which were not at all defensible tended to build clockwise and anticlockwise spiral staircases as matching pairs, so it wasn't like there was some other sort of massive aversion to stairs in a particular direction.
For perspective, Norman keeps were often built with a large internal cross wall, so even if troops made it through the stair door and swarmed into the room they'd still have to fight their way into the other half of the floor. By the stage these expensive and space consuming walls were defensively relevant, defenders would have already lost outer walls, viable long-term food and water supplies and much of the garrison defending it... and any real chance of holding out. But an invading army would still lose more men storming it; so it functioned as a deterrent.
I've heard this "it's a myth" argument before, but 70% of staircases is quite a large proportion of staircases spiralling in a particular direction which would offer the defender a marginal advantage to be pure coincidence. Particularly when the ratio of clockwise to anticlockwise staircases in Norman castles was about 20:1; it was later generations of castle of builders who added many more anticlockwise stairwells, in an era when individual tower defence was less importance, and builders may have simply forgotten or come to doubt arguments about the defensive advantages of clockwise spirals (the blog's arguments for why spiral staircase defence is rubbish work here of course!). Contemporary cathedrals which were not at all defensible tended to build clockwise and anticlockwise spiral staircases as matching pairs, so it wasn't like there was some other sort of massive aversion to stairs in a particular direction.