At Rome, dogs were used to guard houses, and "Cave canem!" was equally common with our "Beware of the dog!".
"'The Dog at Rome' was a hostile reference to the Pope used by some historic Englishman (I don't remember who, but it was probably not anyone before Henry VIII, or maybe it was Henry himself). Making it the title of a book on Famous Pets of Popes is a clever and delightful touch."
↑A Treatise on the Arts, Manufactures, Manners, and Institutions of the Greek and Romans, Volume 2. Thomas Dudley Fosbroke (1835).