Gerontius (magister militum)
Gerontius (fl. 407–411) was a general of the Western Roman Empire (with the rank of magister militum), who initially supported the usurper Constantine III, later betraying him in favour of another usurper, Maximus of Hispania. Life

Under Constantine III 

Gerontius, probably a Briton by birth, was one of the supporters of Constantine III, a Roman general who revolted against the emperor Honorius in 407, conquering Britain, Gaul, Germania, and Hispania. Constantine's control of Hispania was challenged by the revolts of Didymus and Verenianus, cousins of Honorius. In early 408, Constantine sent an army against the rebels, headed by his son Constans and commanded by Gerontius. After losing his first battle against the rebels, Gerontius recalled additional forces from Gaul and won an important victory in Lusitania, where Didymus and Verenianus were captured. Constans escorted the prisoners back to Gaul, while Gerontius remained in Hispania, in command of the local troops. Usurpation of Maximus 

In late spring 409, Gerontius rebelled against Constantine, who was now officially recognized as co-emperor by Honorius, and appointed his relative Maximus as emperor. He moved to Tarraco, but left the city to oppose Constans's invasion. Constantine had just elevated Constans to Augustus and sent him to Hispania with loyal troops in response. The reasons for Gerontius's rebellion are unclear. It is possible that Constans's elevation to the throne was a result of Gerontius's rebellion, but it is also possible that the general rebelled just because of Constans's appointment. To counteract Constantine, Gerontius allied with Vandals, Alans, and Suebi. A Frankish revolt occupied Constantine, who was forced to reduce his pressure on Gerontius, and the Franks and their allies entered Hispania, where they became a problem for Gerontius. Gerontius successfully defended himself against Constans during 410. In 411, he successfully besieged and captured Constans in Vienne, executing him. He then moved on Arelate, where he besieged Constantine. However, while Constantine was still resisting, Honorius's general Constantius arrived from Italy with an army. Most of Gerontius's soldiers defected to Constantius and was obliged to flee back to Hispania with a few loyal supporters. According to Sozomen, the remaining troops turned on Gerontius once they knew of Gerontius's defeat, and blocked Gerontius and his wife into a house. Gerontius attempted to keep the aggressors away by shooting arrows at them from the roof. When his arrows ran out, the soldiers set fire to the house. Hopelessly defeated, he killed his wife before committing suicide. References

Sources 
 Kulikowski, Michael, Late Roman Spain and Its Cities, Johns Hopkins University Press, 2004, , p. 157-160. 411 deaths
5th-century Romans
Ancient Roman military personnel who died by suicide
Generals of Constantine III
Magistri militum
Year of birth unknown