Although armies existed in ancient Egypt, China, India, and Assyria, Greece was the first country known for a disciplined military land force. The Greeks made military service obligatory for citizens and training was rigorous. As a result of Greek military successes, leaders of other nations sought the services of Greek mercenaries. In time, a class of professional soldiers developed. They sold their services to other rulers as well as to wealthy Greeks who chose to avoid required military service (see Xenophon).
Like the Greek armies, the Roman army was originally composed of citizen soldiers. As the Roman Empire expanded, a professional standing army came into being; it became increasingly composed of barbarian mercenaries. The Roman army was divided into legions, each of which included heavy and light infantry, cavalry, and a siege train. The army became a political force that often determined who ruled the empire.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.