How wide are these stairs, typically? Because I've been in a staircase built by hand out of stone (and yes, I was given this exact explanation for why it was built clockwise, despite it being in Carmel, California, which is not exactly a hotspot for medieval sieges). And a lot of what people are talking about here is laughably irrelevant if the stairs were as steep and narrow as that one was.

It was tight. I didn't have much trouble climbing it, but I'm not sure I could have navigated it at all wearing armor. Falling down the stairs was not an issue because you'd just fall against the curved wall. Passing by other people? Hahaha. Maybe if you were trying to play Medieval Twister.

The defender advantage argument was viscerally satisfying, because you could so easily imagine how impossible it would be to do anything with the inward hand. Which is probably mostly evidence for why the myth persists, whether it is true or false. Though that itself could have applied to the builders or customers of times past. You can build them one way or the other, and here's a satisfying explanation for one even if it pertains to a situation that never happens, so... why not go with clockwise?

Then again, if I were to speculate, I would wonder why the fixation on sieges? If the defensibility argument were true, couldn't it apply to other situations like an attack by the populace or staff? The lord's personal guard might still appreciate the edge.

I can't help but think that carrying beer, torches, or chamber pots ought to be a bigger part of the justification, though.