> 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.
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?