When in Rome...

... you're at risk for getting stabbed in the buttocks.

The practice even has its own slang name in the local Roman dialect - "puncicate". But why is the backside targeted?

According to those who have researched the subject, a stab wound in the buttocks may be chosen as it is seen as not likely to be life-threatening, but is humiliating and painful for the victim.

This explanation makes sense:

The practice has also been linked by some academics to medieval first-blood duels, says football writer Gabriele Marcotti. "In the duels the first person to draw blood from their opponent was the winner. Because they fought facing each other, drawing blood by stabbing your opponent's buttocks was considered a great skill.

"But while it's difficult to stab someone in the backside with a sword in that context it's not difficult to do it with a knife from behind, which is what happens these days. 'Puncicate' is not about skill, whatever those who do it like to think."