In the novel Satyricon the Latin writer Petronio describes a scene where the protagonist is frightened by a very realistic mosaic representing a ferocious guard dog and a warning: Cave Canem.
"...While Trimalchio (*) was being carried away, a player with a tiny flute approached his head, and as if speaking secretly in his ear, played for him all along the way. We were coming behind, already satiated with refinements, together with Agamemnon.
When we arrived at the door we found a sign posted where it was written: "The slave who goes out without the master's permission will receive a hundred beatings"
Right at the entrance stood a doorman dressed in green with a cherry-colored belt, peeling peas in a silver dish. Above the threshold hung a golden cage with a colorful magpie inside that greeted the guests.
I was looking at these things in amazement, when I had to jump back so suddenly that I almost broke my leg. I had seen on the left, and near the doorman's guard, a large dog tied to a chain, painted on the wall that seemed to be alive, with the words below in all capital letters: BEWARE OF THE DOG. My companions laughed..." (**)
Satyricon, Petronius Arbiter (26 - 66 AD)
(*) trimalcònico adj. (pl. m. -ci), letter. – Worthy of Trimalchio or Trimalchio, a rich but rude freedman who, in the novel Satyricon by the Latin writer Petronius, prepares a spectacular dinner, but annoys the guests with his constant explanations relating to the foods presented and their preparation.
(**) At the entrance to the house, on the floor, were the motto: hello!, and the warning: cave canem!