Wallia made peace with emperor Honorius and accepted a treaty with the Romans. Wallia returned Honorius' sister Galla Placidia to him, and in return Wallia was granted Aquitaine in 417 as a region where the Visigoths would be based as foederati. He established his court in Toulouse, which became the Visigothic capital for the rest of the fifth century.
In 418 he honoured the alliance by invading Spain, where his army destroyed the Siling Vandals and so reduced the numbers Alans living there that the survivors placed themselves under the rule of Gunderic, king of the Asding Vandals.
Wallia earned a great reputation as warrior and was known as a prudent ruler.
Some historical sources say that he was related to Alaric only by marriage.
He was succeeded by Alaric's illegitimate son Theodorid.