Periods of conquest contributed to the Roman economy in a number of ways. The Romans sought to control natural resources and attain wealth from the regions they conquered. By harnessing the revenues of conquest, they could support their goals of keeping the populace fed and the troops paid. In early Rome, the army was a volunteer force mustered during times of conflict. By the time of the empire, however, it had become a standing professionalized force. The Roman legion was the cornerstone of the army. Though its organization changed over time, this military unit consisted of about five thousand soldiers and was commanded by a legate. A legion also included craftspeople and those assisting in building projects. Following the reforms of Augustus, twenty-eight legions were stationed throughout the provinces of the empire and on the frontier. They were numbered but also had nicknames based on their place of origin or service. Since legions could move around the empire, the First German legion might be found in Spain, for example. Soldiers served a sixteen-year term, though this was later raised to twenty, and they were paid a set amount at the end of their service. Soldiers and military staff received a large portion of the wealth secured during wartime, and some were also occasionally promised land taken in the various conflicts that Rome engaged in. Many military engagements were clearly intended to secure resources and capital. For instance, the empire’s grain supply was vastly expanded by its conquest of Egypt in the first century BCE, as well as of Sicily and Sardinia early in Rome’s history. In addition, people captured in conquest were often sold in the Roman slave markets. Since the work of enslaved and freed people was the backbone of Roman industry, enslaved people too contributed to the functioning of the economy. But there were trade-offs in this arrangement. The increasing size of the Roman military and the empire’s expanding frontier made conflict more costly. While earlier in its history, Rome’s soldiers might expect to campaign only part of the year, by the imperial period, conflict had become a regular situation on the frontier. Campaigns could last for months on end, and in some situations wars may have seemed endless. The distance from the city of Rome also contributed to the cost of running the military; far-flung military campaigns were expensive. The machinery of running and paying the army necessitated further conquest, a situation that ultimately strained the Roman military. In addition, there were clearly societal disadvantages to continuous conflict. Though Romans took pride in their military superiority, the loss of life and property must have been a burden for many. Conflict abroad disrupted regional markets that Italy depended on. For example, an interruption in the grain supply in 190 CE resulted in famine and riots in the city of Rome. Elites were largely able to benefit from the economic arrangement of conquest, but those in the lower classes no doubt shouldered the burden of its negative consequences.