"The domestic animal that is most faithful to man is the dog. Stories are told of the faithfulness of dogs:
of a dog that fought robbers that attacked his master, which though badly wounded would not abandon the man's corpse, driving off other beasts and birds;
of a dog in Epirus which recognized its master's murderer in a crowd and pointed him out by barking;
of the 200 dogs of the King of Garamantes which escorted him home from exile and fought anyone who got in the way;
of the dog of a condemned prisoner which refused to leave its master, tried to put food in the dead man's mouth, and when the corpse was thrown in the river, tried to keep it afloat."
This from the Roman scholar Pliny the Elder, in his book Natural History -- written in the first century AD. I found this in a wonderful site called Medieval Bestiary.