The first successful attempt to convert them was made, under the powerful protection of Pippin of Heristal, by Willebrord, a Northumbrian monk, who became, A.D.
The conquest of the Frisians by the Franks was begun by Pippin (Pepin) of Heristal in 689 and practically completed by Charles Martel, though they were not entirely brought into subjection until the time of Charlemagne.
The virtual independence of these German tribes lasted until the union of Austrasia and Neustria in 687, an achievement mainly due to the efforts of Pippin of Heristal, who soon became the actual, though not the nominal, ruler of the Frankish realm.
It was during the time of Pippin of Heristal and his son and grandson that the conversion of the Germans to Christianity was mainlyeffected.
Towards the end of the 7th century Pippin II., called incorrectly Pippin of Heristal, secured a preponderant authority in Austrasia, marched at the head of the Austrasians against Neustria, and gained a decisive victory at Tertry, near St Quentin (687).