<P> During this period the Republican system of citizen - conscription was replaced by a standing professional army of mainly volunteers serving standard 20 - year terms (plus 5 as reservists), although many in the service of the empire would serve as many as 30 to 40 years on active duty, as established by the first Roman emperor, Augustus (sole ruler 30 BC--AD 14). Under Augustus there were 28 legions, consisting almost entirely of heavy infantry, with about 5,000 men each (total 125,000). This had increased to a peak of 33 legions of about 5,500 men each (c. 180,000 men in total) by AD 200 under Septimius Severus . Legions continued to recruit Roman citizens, mainly the inhabitants of Italy and Roman colonies, until 212 . Regular annual conscription of citizens was abandoned and only decreed in emergencies (e.g. during the Illyrian revolt 6--9 AD). Legions were now flanked by the auxilia, a corps of regular troops recruited mainly from peregrini, imperial subjects who did not hold Roman citizenship (the great majority of the empire's inhabitants until 212, when all were granted citizenship). Auxiliaries, who served a minimum term of 25 years, were also mainly volunteers, but regular conscription of peregrini was employed for most of the 1st century AD . The auxilia consisted, under Augustus, of about 250 regiments of roughly cohort size, that is, about 500 men (in total 125,000 men, or 50% of total army effectives). Under Severus the number of regiments increased to about 400, of which about 13% were double - strength (250,000 men, or 60% of total army). Auxilia contained heavy infantry equipped similarly to legionaries, and almost all the army's cavalry (both armoured and light), and archers and slingers . </P> <P> The Late Roman army (284--476 AD and its continuation, in the surviving eastern half of the empire, as the East Roman army to 641). In this phase, crystallised by the reforms of the emperor Diocletian (ruled 284--305 AD), the Roman army returned to regular annual conscription of citizens, while admitting large numbers of non-citizen barbarian volunteers . However, soldiers remained 25 - year professionals and did not return to the short - term levies of the Republic . The old dual organisation of legions and auxilia was abandoned, with citizens and non-citizens now serving in the same units . The old legions were broken up into cohort or even smaller sizes . At the same time, a substantial proportion of the army's effectives were stationed in the interior of the empire, in the form of comitatus praesentales, armies that escorted the emperors . </P> <P> The Middle Byzantine army (641--1081 AD) was the army of the Byzantine state in its classical form (i.e. after the permanent loss of its Near Eastern and North African territories to the Arab conquests after 641 AD). This army was largely composed of semi-professional troops (soldier - farmers) based on the themata military provinces, supplemented by a small core of professional regiments known as the tagmata . This structure pertained when the empire was on the defensive, in the 10th century the empire was increasingly involved in territorial expansion, and the themata troops became progressively more irrelevant, being gradually replaced by' provincial tagmata' units and an increased use of mercenaries . </P> <P> The Komnenian Byzantine army was named after the Komnenos dynasty, which ruled from 1081--1185 . This was an army built virtually from scratch after the permanent loss of Byzantium's traditional main recruiting ground of Anatolia to the Turks following the Battle of Manzikert in 1071, and the destruction of the last regiments of the old army in the wars against the Normans in the early 1080s . It survived until the fall of Constantinople to the Western crusaders in 1204 . This army had a large number of mercenary regiments composed of troops of foreign origin such as the Varangian Guard, and the pronoia system was introduced . </P>

Describe the roman senate and list 3-4 characteristics