Editing Roman legion (section)

=== Early Empire (27 BC–AD 284) ===
{{Main|Imperial Roman army}}
{{Hatnote|See also [[List of Roman legions#Early Empire legions|List of Roman legions of the early Empire]]<br />
See also [[List of Roman army unit types#Sub-units of the Roman legion|Sub-units of the Roman legion]]}}
[[File:Roman-legions-14-AD-Centrici-site-Keilo-Jack.jpg|thumb|350px|Map of Roman legions by 14 AD]]
[[File:Roman Empire 125 political map.svg|thumb|350px|Roman Empire and legions in 125 AD near its maximum extent]]

Generals, during the recent Republican civil wars, had formed their own legions and numbered them as they wished. During this time, there was a high incidence of ''Gemina'' (twin) legions, where two legions were consolidated into a single organisation (and was later made official and put under a ''[[legatus]]'' and six ''[[Dux|duces]]''). At the end of the civil war against [[Mark Antony]], Augustus was left with around fifty legions, with several double counts (multiple Legio Xs for instance). For political and economic reasons, Augustus reduced the number of legions to 28 (which diminished to 25 after the [[Battle of the Teutoburg Forest|Battle of Teutoburg Forest]], in which three legions were completely destroyed by the [[Germanic peoples|Germanics]]).

Beside streamlining the army, Augustus also regulated the soldiers' pay. At the same time, he greatly increased the number of auxiliaries to the point where they were equal in number to the legionaries. He also created the [[Praetorian Guard]] along with a permanent [[Roman navy]] where served the ''liberti'', or freed slaves.
The legions also became permanent at this time, and not recruited for particular campaigns. They were also allocated to static bases with permanent ''[[castra]] legionaria'' (legionary fortresses).

Augustus' military policies proved sound and cost effective, and were generally followed by his successors. These emperors would carefully add new legions, as circumstances required or permitted, until the strength of the standing army stood at around 30 legions (hence the wry remark of the philosopher [[Favorinus]] that ''It is ill arguing with the master of 30 legions''). With each legion having 5,120 legionaries usually supported by an equal number of auxiliary troops (according to Tacitus), the total force available to a legion commander during the [[Pax Romana]] probably ranged from 11,000 downwards, with the more prestigious legions and those stationed on hostile borders or in restive provinces tending to have more auxiliaries. By the time of the emperor [[Septimius Severus|Severus]], 193–211, the auxiliaries may have composed 55 to 60% of the army, 250,000 of 447,000. Some legions may have even been reinforced at times with units making the associated force near 15,000–16,000 or about the size of a modern [[Division (military)|division]].

Throughout the Imperial era, the legions played an important political role. Their actions could secure the empire for a [[Roman usurper|usurper]] or take it away. For example, the defeat of [[Vitellius]] in the [[Year of the Four Emperors]] was decided when the [[Danube|Danubian]] legions chose to support [[Vespasian]].

In the Empire, the legion was standardised, with symbols and an individual history where men were proud to serve. The legion was commanded by a ''[[legatus]]'' or ''legate''. Aged around thirty, he would usually be a senator on a three-year appointment. Immediately subordinate to the legate would be six elected ''military tribunes'' – five would be staff officers and the remaining one would be a noble heading for the Senate (originally this tribune commanded the legion). There would also be a group of officers for the medical staff, the engineers, record-keepers, the ''praefectus castrorum'' (commander of the camp) and other specialists such as priests and musicians.