Origins of Caesar\'s 10th legion

[Praefectusclassis]

RE Smith, Service in the Post Marian Army, p.35 states that those 16 years were indeed the legal upper limit. It seems very likely that what Augustus did in his famous army 'reforms' was just to adapt the new situation to as many old regulations as possible. 16 years was not randomly chosen, but went back to the number of years a Roman citizen was liable for. IF Legio X was raised from tirones in 64 BC, that would make legally conscious Roman citizens clamor for discharge in 48 BC and, after 6 years of service, make the legion a veteran legion by 58.