answer:The size of a typical legion varied widely throughout the history of ancient Rome, with complements of 4,200 legionaries in the republican period of Rome (split into 35 maniples of 120 legionaries each), to around 5,500 in the imperial period (split into 10 cohorts of 480 men each, with the first cohort at double strength: the remaining 220 being cavalry 120 and technical staff). As legions were not standing armies until the Marian reforms (c. 107 BC), and were instead created, used, and disbanded again, several hundred legions were named and numbered throughout Roman history. To date, about 50 have been identified. In the time of the Early Roman Empire, there were usually about 25–35 standing legions plus their Auxiliaries, with more raised as needed. See List of Roman legions for a catalogue of known late republic, early Empire and late Empire legions, with dates in existence, emblem and locations of deployment.
http://en.wikipedia.org/wiki/Roman_legion