EAGLE, in Heraldry, is accounted one of the most noble bearings in armoury; and, according to the learned in this science, ought to be given to none but such as greatly excel in the virtues of generosity and courage, or for having done singular services to their sovereigns; in which cases they may be allowed a whole eagle, or an eagle naissant, or only the head or other parts thereof, as may be most agreeable to their exploits.
The eagle has been borne, by way of ensign or standard, by several nations. The first who seem to have assumed the eagle are the Persians; according to the testimony of Xenophon. Afterwards it was taken by the Romans; who, after a great variety of standards, at length fixed on the eagle, in the second year of the consulate of C. Marius: till that time, they used indifferently wolves, leopards, and eagles, according to the humour of the commander.
The Roman eagles, it must be observed, were not painted on a cloth or flag; but were figures in relief, of silver or gold, borne on the tops of pikes; the wings being displayed, and frequently a thunderbolt in their talons. Under the eagle on the pike, were piled bucklers, and sometimes crowns. Thus much we learn from the medals.
Constantine is said to have first introduced the eagle with two heads, to intimate, that though the empire seemed divided, it was yet only one body. Others say, that it was Charlemagne who resumed the eagle as the Roman ensign, and added to it a second head; but that opinion is destroyed, by an eagle with two heads, noted by Lipsius, on the Antonine column; as also by the eagle's only having one head on the seal of the golden bull of the emperor Charles IV. The conjecture, therefore, of F. Menestrier appears more probable, who maintains, that as the emperors of the East, when there were two on the throne at the same time, struck their coins with the impression of a cross, with a double traverse, which each of them held in one hand, as being the symbol of the Christians; the like they did with the eagle in their ensigns; and instead of doubling their eagles, they joined them together, and represented them with two heads. In which they were followed by the emperors of the West.
F. Papebroche wishes that this conjecture of Menestrier were confirmed by ancient coins; without which, he rather inclines to think the use of the eagle with two heads to be merely arbitrary; though he grants it probable, that it was first introduced on occasion of two emperors on the same throne.
The eagle on medals, according to M. Spanheim, is a symbol of divinity and providence; and, according to all other antiquaries, of empire. The princes on whose medals it is most usually found, are the Ptolemies and the Seleucides of Syria. An eagle with the word CONSECratio, expresses the apotheosis of an emperor.