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.
Legionary
As Augustus consolidated power in 27BC and founded the Principate, he further professionalized the Roman legionary. Under him, a legionary's term of service was raised to 25 years (before that, a legionary's average term of service was only 10 years) and pay was standardized throughout the legions. Other than the gradual provincialization of recruits and the evolution of some military equipment, Roman legionaries would remain broadly unchanged until the end of the Pax Romana. These legionaries would expand Rome's borders to include lower Britannia, Dacia, North Africa, and more through military campaigns under Augustus and future emperors.