The eagle first appears as a military standard among the Persians. It was one of the first military standards of the Romans, having been adopted in 104 B. C., as the chief emblem to be borne at the head of the legions. Eagles were sometimes of gold, but oftener of silver, and were carried on the top of a spear. The eagle of Russia to-day is double-headed, and is the national military symbol. The eagles of Prussia and of the United States are single-headed. That of the United States, the bald eagle with wings displayed, is the national emblem and was adopted in 1785.