"There on the left as one entered...was a huge dog with a chain round its neck. It was painted on the wall and over it, in big capitals, was written: Beware of the Dog."
Petronius, Satyricon (XXIX)
This mosaic of a guard dog, one of several in Pompeii, is on the floor of the entrance hall to the House of the Tragic Poet, which also is known for its fresco of the Sacrifice of Iphigenia.
Reference: The picture comes from What Life Was Like: When Rome Ruled the World: The Roman Empire, 100 BC-AD 200 (1997) by the Editors of Time-Life Books.
