I think this is the case. A siege is just one scenario out of many where someone could be attacking you in a castle. I have also been in several castles in UK where the penultimate step before the roof is deliberately 1 inch higher than all the others. The story is that if you were being chased up the stairs your attacker would trip over onto the roof and you could easily dispatch him. Would this author also claim the rationale of this feature as a myth, and that they just made the same measurement mistake in multiple castles?
Incidentally, if you're not aware of it, a 1 inch difference in stair height will almost certainly make you trip up. I did myself when I was climbing them at first.
Also the notion that once attackers were in a castle it's all over is not true. Late medieval castles were designed to be modular, layered and flexibly defensible. The enemy might get into one part, but you could retreat to another part and defend that. Might give you enough time to be relieved by an external force. Have a look at Caerphilly castle as an example: https://en.wikipedia.org/wiki/Caerphilly_Castle
Finally, it seems that no real explanation is given to the bias towards building clockwise staircases. Why would this be the case? Doesn't it just mean that wherever possible they would build the staircase clockwise because there was some inherent advantage?
Well, if that was practice, then attackers would know about that. Also, there is possibility for someone who is running away to trip.
However, there is a hole in logic - what roof has any strategical advantage? Perhaps, one person will trip - rest of 99 out of 100, that are chasing you would eventually go through. Were there any further routes from the roof? Death from falling is my guess...
The reason why there would be higher step for roof, might have more something to do with dampness and to prevent wearing of that step, or to prevent leakage from the roof, that would stream down the stairs. SAeriously, who is making those stories, that makes no sense and who are so gullible to believe them? Are there any of those stairs seen on money? Drunks from my native town were telling stories about oak(which is recently planted - no more than 50 years), ythat they claimed were pictured on money... usually they wanted to claim that money after a story, if someone wanted to disprove it and brought their vallet out...
I think your mental model of a castle is not quite correct. It's not necessarily a simple stone box. A lot of roofs lead to higher points, or to walls.
Your mental model of what can happen in a castle is also not complete. It's not just sieges, there are any number of reasons someone could be chasing you. It could just be one assailant.
Finally, perhaps I didn't describe the step well enough. The step is not the top one, it is the second one down, and the face of it is around 2cm higher than all the other steps. It wouldn't make any difference to the drainage. Don't get angry that there are features of castles that are not adequately explained, and some people try to explain them.
> The story is that if you were being chased up the stairs your attacker would trip over onto the roof and you could easily dispatch him
Wouldn't it be equally as likely that while running away in panic, you'd trip on the top stair yourself?
In my opinion, a more realistic explanation is that on plan the stairs were all the same height. But when the builders reached the top, they realised that the roof was an inch higher than planned and just made the final step a bit taller to make the difference?
If you know the step is there, you get used to avoiding tripping.
It's not the final step, it's the penultimate step. Also everything else in the castle is straight and true, which would imply they knew how to measure things accurately enough. It's also in more than one castle.
Incidentally, if you're not aware of it, a 1 inch difference in stair height will almost certainly make you trip up. I did myself when I was climbing them at first.
Also the notion that once attackers were in a castle it's all over is not true. Late medieval castles were designed to be modular, layered and flexibly defensible. The enemy might get into one part, but you could retreat to another part and defend that. Might give you enough time to be relieved by an external force. Have a look at Caerphilly castle as an example: https://en.wikipedia.org/wiki/Caerphilly_Castle
Finally, it seems that no real explanation is given to the bias towards building clockwise staircases. Why would this be the case? Doesn't it just mean that wherever possible they would build the staircase clockwise because there was some inherent advantage?