Ammianus Marcellinus about Constantius II -- By Michel Mulder
One of the main sources on Constantius II is Ammianus Marcellinus. Constantius II was made Ceasar in 324 AD by his father Constantine the Great. When his father died, in 337, he was campaigning in the east of the empire. Together with his brothers Constans I and Constantine II he became the successor of his father after a thorough family-assassination which only his cousins Julian and Gallus survived. A number of women, children and retainers were killed, all in some way related to the Constantinian imperial family and household. Events in history are not always recorded, simply because it is kept a secret by those involved. In any case, Constantius became Augustus over the eastern parts of the empire, and after the death of Constantine II and Constans I, Constantius II obtained their sphere.
In his life, Constantius II spent most of his time campaigning. Due to troubles on the northern borders of the empire and the renewed aggression of the Persian king Sapor II in the east, he had a tremendous task in keeping the borders unviolated. Internal affairs too played a large part in the policymaking of Constantius II. He seemed to be a very conspicuous person.
Policy of Constantius according to Ammianus
After Constantius II became sole ruler of the Roman empire (350), he had to divide his troops, and therefore, his attention to several parts of this vast empire. On one side, the Persians were causing a lot of disturbance by continuing attacks on cities on Roman territory. Constantius fortified several cities (18.9.1-2), so that they could withstand lasting attacks. The Persian king Sapor was able to take the initiative, after the sudden death of Constantine, and Constantius II was thus forced on the defensive (Barnes, 1998, 136-7).
On the northern border Constantius II was forced to follow the same policy. This was due to internal affairs in this area. The usurpators Magnentius and Vetranio were a serious threat to the power of Constantius. After 350, the uprisings of two other usurpators Nepotian (in 350) and Silvanus (355) were to be dealt with. They were put down by opponents of the emperor, and Constantius himself (15.5.1-34).
To diminish the Germanic threat, Constantius appointed his cousin Julian as Caesar and military commander of Gaul (15.8). Julian was not made sole ruler of Gaul, Constantius divided military and civil authority, not an uncommon feature of late Roman history.
The victories over the usurpators were the cause of the erection of several triumphal arches, to honour Constantius. Now, although this emperor in foreign wars met with loss and disaster, yet he was elated by his success in civil conflicts and drenched with awful gore from the internal wounds of the state, Ammianus says, and he continues in his critical review: It was on this unworthy rather than just or usual ground that he erected triumphal arches and added records of his deeds, that men might read of him so long as those monuments could last (21.16.15). It was usual for emperors to celebrate a triumph only over foreign enemies, but Constantius celebrated victories over fellow Roman cives.