Cave canem is a Latin phrase that literally means "Be careful of the dog". It was written at the entrance to the houses to warn that there was a potentially dangerous dog inside. The practice is very similar to that in use today.

The inscription can be found in a famous mosaic found in the archaeological excavations of Pompeii, on the entrance floor of the House of the Tragic Poet. Another mosaic, without an inscription, in which the animal is represented on the chain near a semi-open door is also visible in Pompeii at the entrance to the Casa di Paquio Proculo.

Finally, a well-known mosaic, also found in the House of Orpheus, is kept in the National Archaeological Museum of Naples.