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.
History of the Roman Empire
Meanwhile, Gratian, Valentinian II and Theodosius were joined by a fourth Augustus. Theodosius proclaimed his oldest son Arcadius an Augustus in January 383 in an obvious attempt to secure succession. The boy was still only five or six years old and held no actual authority. Nevertheless, he was recognised as a co-ruler by all three Augusti.