On the southern border of the canton of the Allobroges at the confluence of the Isere with the Rhone, on the 8th of August 633, the battle was fought which decided the mastery of southern Gaul.

King Betuitus, when he saw the innumerable hosts of the dependent clans marching over to him on the bridge of boats thrown across the Rhone and the Romans who had not a third of their numbers forming in array against them, is said to have exclaimed that there were not enough of the latter to satisfy the dogs of the Celtic army.

Nevertheless Maximus, a grandson of the victor of Pydna, achieved a decisive victory, which, as the bridge of boats broke down under the mass of the fugitives, ended in the destruction of the greater part of the Arvernian army.

The Allobroges, to whom the king of the Arverni declared himself unable to render further assistance, and whom he advised to make their peace with Maximus, submitted to the consul; whereupon the latter, thenceforth called Allobrogicus, returned to Italy and left to Ahenobarbus the no longer distant termination of the Arvernian war.

Ahenobarbus, personally exasperated at king Betuitus because he had induced the Allobroges to surrender to Maximus and not to him, possessed himself treacherously of the person of the king and sent him to Rome, where the senate, although disapproving the breach of fidelity, not only kept the men betrayed, but gave orders that his son, Congonnetiacus, should likewise be sent to Rome.