Once in Gaul, Athaulf opened negotiations with a new usurper, the Gallic Jovinus. But while on his way to meet Jovinus, Athaulf came across Sarus and some of his men. Athaulf attacked, captured, and later executed Sarus, continuing the feud between their families that had begun with Sarus and Alaric. Jovinus then named his brother Sebastianus (Sebastian) as Augustus (co-emperor). This offended Athaulf, who hadn't been consulted. So he allied his Visigoths with Honorius. Jovinus' troops were defeated in battle, Sebastianus was captured, and Jovinus fled for his life. Athaulf then turned Sebastianus over for execution to Honorius' Gallic praetorian prefect (provincial governor), Claudius Postumus Dardanus. After this, Athaulf besieged and captured Jovinus at Valentia (Valence) in 413, sending him to Narbo (Narbonne), where he was executed by Dardanus.