2. A Briton, one of the two generals appointed by the usurper Constantine to command his army, after the death of his first generals, Neviogastes and Justinian. The reputation of Gerontius and his colleague (Edovinchus, a Frank) is attested by the fact that Sarus, whom Stilicho had sent to attack Constantine, and who was besieging the usurper in Vienna (Vienne), in Gaul, prepared for a retreat when he heard of their appointment, and escaped with loss and difficulty into Italy (A. D. 408).

When Constans, son of Constantine, whom his father had sent to subdue Spain, returned, after effecting the subjugation of that country, to his father in Gaul, he left Gerontius to guard the passes of the Pyrenees. Being sent back again, he took Justus with him as his general, and this offended the proud spirit of Gerontius, and induced him to revolt (A. D. 408). His first step was to negotiate with the barbarians (probably the Vandals, Alans, and Suevi), who were ravaging Gaul and Spain, and the troubles he excited appear to have recalled Constantine from Italy, whither he had gone apparently, to assist, but really to dethrone Honorius. After his return, he was attacked by Gerontius. The insurgents had driven Constans out of Spain, where Gerontius had declared his friend (or perhaps his servant) Maximus emperor, and left him at Tarragona; and Constans being taken at Vienna (Vienne), was slain by order of Gerontius, and Constantine himself was besieged by Gerontius in Arles. But the approach of an army sent by Honorius, under his general Constantius, obliged Gerontius to raise the siege, and being abandoned by the greater part of his troops, who went over to Constantius, he fled towards Spain. The troops there, however, looking upon him as quite ruined, conspired to kill him. Attacked by superior numbers, lie defended himself most resolutely, and killed many of his assailants; but finding escape impossible, he put an end to his own life, after first killing, at their own request, his wife, and a faithful Alan friend or servant, who accompanied him. The wife of Gerontius is expressly said by Sozomen to have been a Christian; the silence of the historian leads us to suppose that Gerontius himself was a heathen. His revolt, by preventing Constantine from holding the barbarians in check, led to the assumption of independence in self-defence by the Britons and Armoricans. (Zosim. 6.1-6; Oros. 5.22; Prosp. Aquit. Chron.; Beda, Hist. Eccl. 1.11; Sozom. H. E. 9.12, 13; Olympiod. apud Phot. Bibl. cod. 80.)