Stairwells were often very carefully designed in Medieval Castles. Stairwells that curved up to towers often curved very narrowly and in a clockwise direction. This meant that any attackers coming up the stairs had their sword hands (right hand) against the interior curve of the wall and this made it very difficult for them to swing their swords. Defenders had their sword hands on the outside wall, which meant they had more room to swing. Another ingenious design of stairs was that they were designed with very uneven steps. Some steps were tall and other steps were short. The inhabitants, being familiar with the uneven pattern of the stair heights could move quickly up and down the stairs but attackers, in a dimly lit stairwell, would easily fall and get bogged down in the stairwells. This made them vulnerable to attacks and slowed their attacks down significantly.
--Will Kalif, The Vintage News, on the ingenuity inspired by war