Firmus (4th-century usurper)

Firmus (died 375) was a Roman usurper under Valentinian I.

Firmus was the son of the Moorish (Berber) prince Nubel, a powerful Roman military officer, as well as a wealthy Christian. When Nubel died, Firmus killed his half-brother Zammac, who had illegitimately appropriated of Nubel's wealth, and became successor to his father.

Between 372 and 375, Firmus revolted against the comes Africae Romanus, who was a supporter of Zammac. The misbehaviour of Romanus, who had neglected protection from African tribes to Roman cities that had refused the payment of bribes, had worsened the situation in Africa Province in the 360s. The revolt of Firmus against Romanus forced Valentinian to take action against both his officer and the African rebel.

When Valentinian sent his magister militum Theodosius (father of Theodosius I) to depose Romanus, Firmus tried to find a compromise with him, but Theodosius refused peace to Firmus, who had proclaimed himself emperor.

With the support of the Berber tribes, Firmus obliged Theodosius to a bloody and hopeless campaign. In the end, however, Firmus was betrayed by one of his supporters, and chose suicide over capture.

Firmus supported the Donatists against the Nicene faith. Firmus ordered the killing of the Nicene inhabitants of Rusuccuru, and after his death, Valentinian issued laws against the Donatists.

It is also possible that this Firmus was the basis on which the author of Historia Augusta modeled the improbable Firmus, usurper against Aurelian.

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