Gildo was a Moor by birth. Being a son of King Nubel (regulus per nationes Mauricas), he was brother to Firmus. His other brothers were called Mascezel, Mazuca, Sammac, and Dius. He had a sister named Cyria.
In 375, his brother Firmus revolted against Valentinian I, Gildo stayed loyal to the emperor and helped suppress the revolt, he was rewarded with the immense patrimony confiscated from his brother. In 386, Theodosius I appointed Gildo Comes Africae and Magister utriusque militiae per Africam, as reward for his support to his father Theodosius the Elder in the suppression of Firmus' revolt. By that time, Gildo ruled the entirety of Northern Africa.
After the death of Theodosius and the rise to the throne of his sons, Arcadius and Honorius, Gildo saw an increase in his importance: the province of Africa, in fact, became entrusted with the grain supply to the city of Rome, a role played by Egypt until the split of the Empire into two halves. Incited by the political machinations of the eunuch Eutropius, Gildo seriously entertained the notion of joining the Eastern Roman Empire by pledging fidelity to Arcadius. The possibility of losing the granary of Rome led to civil turmoil in the city, and acting on an appeal by Stilicho, the Roman Senate declared Gildo an "enemy of the State" and started a war against him.
At the same time, Gildo had a quarrel with his brother Mascezel, who was obliged to flee to the court of Honorius; Gildo took revenge on his brother by killing his two sons. Mascezel was entrusted by Stilicho with the command of the war against Gildo and given the command of a chosen body of Gallic veterans, who had lately served under the standard of Eugenius. Landed with his few troops in Africa, he camped in front of a large Moorish camp. Gildo's was defeated and obliged to flee in a small boat, hoping to reach the friendly shores of the Eastern Roman Empire. However, unfavourable winds drove the vessel back to the harbour of Tabraca, where the inhabitants were eager to display their new loyalty by throwing Gildo in the dungeons. To avoid the revenge of his brother, Gildo committed suicide by hanging.
After his defeat, Gildo's estates were confiscated and became imperial property. They were so vast that a government position, the Count of Gildo's Patrimony (comes Gildoniaci patrimonii), was created to manage them.
Gildo's family had a marriage connection with the Roman imperial family. Gildo had a daughter named Salvina. Salvina married Nebridius, who was the nephew of Flaccilla. Flaccilla was the first wife of the Emperor Theodosius I.
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- Jones, A.H.M.; Martindale, J.R.; Morris, J. (2 March 1971). Prosopography of the Later Roman Empire, Volume I. p. 633. ISBN 978-0521072335.
- Gibbon reports the units that formed the 5,000 soldiers strong military body:
These troops, who were exhorted to convince the world that they could subvert, as well as defend, the throne of an usurper, consisted of the Jovian, the Herculian, and the Augustan legions; of the Nervian auxiliaries; of the soldiers who displayed in their banners the symbol of a lion; and of the troops which were distinguished by the auspicious names of Fortunate and Invincible.— Edward Gibbon, The Decline and Fall of the Roman Empire
- Jones, A.H.M.; Martindale, J.R.; Morris, J. (7 March 1971). Prosopography of the Later Roman Empire, Volume I. p. 396. ISBN 978-0521072335.
- Platts, John, s.v. "Gildo", A New Universal Biography, Sherwood, Jones, and Co., 1826