Nubel was a powerful Northern African, a Roman military officer, and a Christian. Upon his death in the early 370s, one of his sons, Firmus, killed his half-brother, Zammac, illegitimate heir to Nubel's estate. While illegitimate, Zammac was the son of Nubel most favored by Romanus, the Roman imperial administrator in Africa.
Reasonably, Firmus feared for his safety at the hands of the Roman administrator who had long mismanaged Roman properties in Africa. Romanus refused to defend Tripolitania against raids by other African tribes because Lepcis (one of the 3 major towns of Tripolitania) had failed to send Romanus enough booty to buy his protection. When the Tripolitanians complained to Rome, Romanus diverted the blame and caused the execution of many prominent Africans.
Firmus revolted against Rome.
Emperor Valentinian sent his magister militium, Theodosius the Elder (father of Emperor Theodosius I), to Africa to investigate charges of criminal activity by Romanus and to put down the revolt by Firmus. Upon his arrival, Theodosius arrested Romanus.
With the removal of the threat posed by Romanus, Firmus, who had been proclaimed emperor by his troops (making him a usurper), sought terms with the Roman military commander. Theodosius wouldn't listen to the traitor. Theodosius had promised prominent African provincials who were still loyal to Rome that he wouldn't put a strain on their coffers. Instead, since Africa was Rome's breadbasket, he would take food from Firmus' supporters.
Firmus, who had many more troops than Theodosius, asked for peace 3 times, but in vain. Eventually and despite the numerical odds against him, the Roman leader defeated Firmus' troops, with the help of a third son of Nubel, Firmus' brother Gildo. Firmus then committed suicide.
Gildo was honored by being named comes per Africam (field commander of Africa) under the Roman usurper Magnus Maximus. Magnus Maximus was called a usurper because after serving with Theodosius the Elder in Africa and following a succession of military accomplishments in the Danube and Britain he was proclaimed emperor by his troops -- as had happened with Firmus. Gildo was also tied to the imperial family in Rome through marriage.
When Emperor Theodosius I died, and Honorius, aided by Stilicho, ruled the West (which technically controlled the provinces in Africa), Gildo sought greater independence. He thought he might be better off under the emperor of the East, Arcadius. Arcadius and the eastern court welcomed him, but the western empire couldn't accept the loss of its African granaries. When, in 397, Gildo forbade ships to sail from Africa to Rome, the western empire took this as a declaration of war.
Stilicho stepped in. He arranged an alternate food supply to tide the empire through the winter and then urged the senate to declare Gildo a public enemy. It did so and allotted an army of about 10,000. Under the command of yet another son of Nubel, Mascezel, the Roman troops set sail.
Gildo commanded 70,000 men, including troops provided by neighboring African tribes. Even though the Africans had 7 times the manpower of the Romans, they offered little resistance. When he realized defeat was inevitable, Gildo tried to escape, but was caught and killed.
Mascezel was received in Rome as victor of the Gildonic War, but his honor was short-lived. He was killed or drowned crossing a bridge. Unofficially, Stilicho was blamed.
For more on Stilicho, Arcadius, Theodosius and the Roman Empire in the 4th century, see End of the Empire .