round shield, a spear and a helmet. Ancient Rome The Roman Army had its origins in the citizen army of the Republic, which was staffed by citizens serving mandatory duty for Rome. Reforms turned the army into a professional organization which was still largely filled by citizens, but these citizens served continuously for 25 years before being discharged. The Romans were also noted for making use of auxiliary troops, non-Romans who served with the legions and filled roles that the traditional Roman military could not fill effectively, such as light skirmish troops and heavy cavalry. After their service in the army they were made citizens of Rome and then their children were citizens also. They were also given land and money to settle in Rome. In the Late Roman Empire, these auxiliary troops, along with foreign mercenaries, became the core of the Roman Army; moreover, by the time of the Late Roman Empire tribes such as the Visigoths were paid to serve as mercenaries. Medieval Europe In the earliest Middle Ages it was the obligation of every aristocrat to respond to the call to battle with his own equipment, archers, and infantry. This decentralized system was necessary due to the social order of the time, but could lead to motley forces with variable training, equipment and abilities. The more resources the noble had access to, the better his troops would be. Initially, the words "knight" and "noble" were used interchangeably as there was not generally a distinction between them. While the nobility did fight upon horseback, they were also supported by lower class citizens – and mercenaries and criminals – whose only purpose was participating in warfare because, most often than not, they held brief employment during their lord's engagement. As the Middle Ages progressed and feudalism developed in a legitimate social and economic system, knights started to develop into their own class with a minor caveat: they were still in debt to their lord. No longer primarily driven by economic need, the newly established vassal class were, instead, driven by fealty and chivalry. As central governments grew in power, a return to the citizen armies of the classical period also began, as central levies of the peasantry began to be the central recruiting tool. England was one of the most centralized states in the Middle Ages, and the armies that fought in the Hundred Years' War were, predominantly, composed