Eagle, as a military standard, was adopted by the Romans, and even by nations preceding them in history. The Persians, in the time of Cyrus the Younger, bore an eagle on a spear as a standard. The Romans for some time used the eagle, the wolf, the boar, the horse, and the minotaur for standards, but afterwards abandoned the last four, and confined themselves to the first. - Chambers' Encyclopedia, 1875