of the Principate The regular army of the Principate was established by the founder–emperor Augustus (ruled 30 BC – 14 AD) and survived until the end of the 3rd century. The regular army consisted of two distinct corps, both being made up of mainly volunteer professionals. The elite legions were large infantry formations, varying between 25 and 33 in number, of c. 5,500 men each (all infantry save a small cavalry arm of 120) which admitted only Roman citizens. The auxilia consisted of around 400 much smaller units of c. 500 men each (a minority were up to 1,000 strong), which were divided into approximately 100 cavalry alae, 100 infantry cohortes and 200 mixed cavalry/infantry units or cohortes equitatae. Some auxilia regiments were designated sagittariorum, meaning that they specialised in archery. The auxilia thus contained almost all the Roman army's cavalry and archers, as well as (from the late 1st century onwards) approximately the same number of foot soldiers as the legions. The auxilia were mainly recruited from the peregrini: provincial subjects of the empire who did not hold Roman citizenship, but the auxilia also admitted Roman citizens and possibly barbari, the Roman term for peoples living outside the empire's borders. At this time both legions and auxilia were almost all based in frontier provinces. The only substantial military force at the immediate disposal of the emperor was the elite Praetorian Guard of c. 10,000 men which was based in Rome. The senior officers of the army were, until the 3rd century, mainly from the Italian aristocracy. This was divided into two orders, the senatorial order (ordo senatorius), consisting of the c. 600 sitting members of the Roman Senate and their sons and grandsons, and the more numerous (several thousand-strong) equites or "knights". Hereditary senators and equites combined military service with civilian posts, a career path known as the cursus honorum, typically starting with a period of junior administrative posts in Rome, followed by 5–10 years in the military and a final period of senior positions in either the provinces or Rome. This tiny, tightly-knit ruling oligarchy of under 10,000 men monopolised political, military and economic power in an empire of c. 80 million inhabitants and achieved a remarkable degree of political stability. During the first 200 years of its existence (30 BC – 180 AD), the empire suffered only one major episode of civil strife (the Civil War of