Alaric was succeeded by his brother-in-law Athaulf, husband of Honorius' sister Galla Placidia, who had been seized during Alaric's sack of Rome. Athaulf settled the Visigoths in southern Gaul. After failing to gain recognition from the Romans, Athaulf retreated into Hispania in early 415, and was assassinated in Barcelona shortly afterwards. He was succeeded by Sigeric and then Wallia, who succeeded in having the Visigoths accepted by Honorius as foederati in southern Gaul, with their capital at Toulouse. Wallia subsequently inflicted severe defeats upon the Silingi Vandals and the Alans in Hispania. Periodically they marched on Arles, the seat of the praetorian prefect but were always pushed back. In 437 the Visigoths signed a treaty with the Romans which they kept.