In 718 he appears as the ally of Chilperic II., king of Neustria, who was fighting against the Austrasian mayor of the palace, Charles Martel; but after the defeat of Chilperic at Soissons in 719 he probably made peace with Charles by surrendering to him the Neustrian king and his treasures.
The Austrasian mayors of the palace succeeded in enforcing their authority in the western as well as in the eastern part, and in re-establishing to their own advantage the unity of the Frankish kingdom.
But the Neustrians threw off the Austrasian yoke and entered into an offensive alliance with the Frisians and Saxons.
It was by means of their horsemen that the Austrasian Franks established their superiority over their neighbours, and in time created the Western Empire anew, while from the word caballarius, which occurs in the Capitularies in the reign of Charlemagne, came the words for knight in all the Romance languages.
In 656, at the moment of his accession to power, Sigebert III., the king of Austrasia, had just died, and the Austrasian mayor of the palace, Grimoald, was attempting to usurp the authority.