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.
Cottius
The Roman alliance was established in 13 or 12 BC, and is attested in an inscription in the Arch of Susa, which was erected to commemorate this agreement between 9 and 8 AD. Augustus attended its unveiling. By it Cottius became a client king of Rome, with his authority was reduced in exchange of the retention of his autonomy. While deferring authority to Augustus, he continued to hold his hereditary position in his land. Millar called such an arrangement as a dual sovereignty. Cottius became a Roman citizen, Latinising his name as Marcus Julius Cottius, and was appointed "præfectus civitatium". Areas assigned to this type of prefect were areas newly brought under Roman administration in the Augustan period. These officials oversaw areas with a number of tribes and had a fixed term of office. However, this post in Cottia was permanent and hereditary.