Angrivarii
The wars began in the last years of the reign of Augustus, first emperor of Rome. Augustus died an old but respected man in the year 14 and was celebrated with much pomp and splendor. He left a document to be read to the senate posthumously, expressly forbidding extension of the empire beyond the Rhine. News of the will was welcomed by the Germans, thinking it gave them a free hand in the region. Germanicus found it necessary to pacify the border, which he did by a combination of scorched earth raids and offers of alliance with Rome - in short, stick and carrot. These raids also kept the army of the lower Rhine distracted from the possibility of mutiny, which had broken out on Augustus's death and only been quelled by concessions and executions.
Imperial Roman army
Unlike the Republican legions, which were, in theory at least, temporary citizen-levies for the duration of particular wars, Augustus and his right-hand man Agrippa clearly envisioned their legions as permanent units composed of career professionals. Under the late Republic, a Roman citizen "iunior" (i.e. male of military age: 16–46 years) could legally be required to serve a maximum of sixteen years in the legions and a maximum of six years consecutively. The average number of years served was about ten. In 13 BC, Augustus decreed sixteen years as the "standard" term of service for legionary recruits, with a further four years as reservists ("evocati"). In AD 5, the standard term was increased to twenty years plus five years in the reserves. In the period following its introduction, the new term was deeply unpopular with the troops. On Augustus' death in AD 14, the legions stationed on the rivers Rhine and Danube staged major mutinies, and demanded, among other things, reinstatement of a sixteen-year term. Augustus prohibited serving legionaries from marrying, a decree that remained in force for two centuries. This measure was probably prudent in the early imperial period, when most legionaries were from Italy or the Roman colonies on the Mediterranean, and were required to serve long years far from home. This could lead to disaffection if they left families behind. But from about AD 100 onwards, when most legions were based long-term in the same frontier-province and recruitment was primarily local, the prohibition of marriage became a legal encumbrance that was largely ignored. Many legionaries formed stable relationships and brought up families. Their sons, although illegitimate in Roman law and thus unable to inherit their fathers' citizenship, were nevertheless frequently admitted to legions.