Mike Bishop

At the time, I could see no way of proving this, however attractive it might seem as an explanation. Some years later, I had the opportunity of visiting the Syrian crusader castle known as Qalaat Saladin (formerly called Saone). On the eastern side of the castle, immediately south of the donjon (which is on the right hand side in the photo), is a range of what are often identified as stables, a pillared structure. At each corner of the pillars within these putative stables, there are diagonally-pierced holes.

Orientation may change, but function clearly did not.

Next time you're in Pompeii, instead of looking at the public buildings, private homes, brothels, wall paintings, baths, shops, water supply, latrines, roads ('What have the Romans ever given us?'), take a good long look at the kerb stones instead.