"Dogs are the only animals that are sure to know their masters; and if they suddenly meet him as a stranger, they will instantly recognize him. They are the only animals that will answer to their names, and recognize the voices of the family. They recollect a road along which they have passed, however long it may be. Next to man, there is no living creature whose memory is so retentive. By sitting down on the ground, we may arrest their most impetuous attack, even when prompted by the most violent rage."
Pliny the Elder - Naturalis Historia (the Natural History) VIII.61
Translated by John Bostock, H.T. Riley