Tombstones as Toilets

In Latin II class today we were reading the werewolf story in Chapter 33 of Ecce Romani II. The students thought it odd that the slave and the soldier were walking down the road and then suddenly the slave would have to wait while the soldier went off into the tombstones. I told them to think about it for a moment but not say anything. Lightbulbs went off over a couple of students' heads and the others looked perplexed. I then explained that tombstones would provide some privacy for those needing to relieve themselves. A couple students, not open-minded enough that urinating or defecating anywhere but in a toilet was even in the realm of possibility, didn't believe me. Unfortunately, I was unable to provide evidence. Doing a quick search after class didn't support me either. Certainly I remember requests or curses on tombstones in the ballpark of "Don't pee on me." I'm not making this up, am I?