by his son Redbad, King of the Frisians. While Aldgisl had welcomed Christianity into his realm, Redbad attempted to extirpate the religion and free the Frisians from subjugation to the Merovingian kingdom of the Franks. In 689, however, Redbad was defeated by Pepin of Herstal in the battle of Dorestad and compelled to cede Frisia Citerior (Nearer Frisia, from the Scheldt to the Vlie) to the Franks. The battle of Dorestad took place around 690 by the capital city of the Frisians close to the Rhine. The Franks were victorious in the battle under the Austrasian mayor of the palace, Pepin of Herstal. Dorestad and Utrecht fell into the hands of Pepin, this gave the Franks control of important trade routes on the Rhine to the North Sea. Following this defeat, Redbad retreated to the island of Heligoland. Willibrord, a student of Wilfred's, was sent to christianise the pagan Frisians at the request of Pepin, who had nominal suzerainty over the region. On 21 November 695 Pope Sergius I gave him a pallium and consecrated him as bishop of the Frisians. He returned to Frisia to preach and establish churches, among them a monastery at Utrecht, where he built his cathedral. Willibrord is counted the first Bishop of Utrecht. It is presumed that the influence of the Franks now reached from south of the Oude Rijn to the coast, but this is not entirely clear because the influence of the Frisians over the central river area was not entirely lost. In any case there was a Catholic Church mission to pagan Frisia with a monastery and episcopal see in Utrecht from 695, founded for Willibrord, and a marriage was arranged between Grimoald the Younger the oldest son of Pepin, and Thiadsvind, the daughter of Redbad, in 711. After Pepin died, in 714, Redbad took advantage of the battle for succession in Francia and regained southern Frisia. He made a treaty with the Neustrasian mayor of the palace, Ragenfrid. In 716, the king of the Franks, Chilperic II, and Ragenfrid, the mayor of the palace of Neustria, invaded Austrasia to impose their will on the competing factions there: those of Theudoald and Plectrude, Pepin's heir and widow respectively, and those of Martel himself, newly escaped from Plectrude's Cologne prison and acclaimed mayor of the palace of Austrasia. Simultaneously Redbad, King of Frisia invaded Austrasia, forcing Saint Willibrord and his monks to