Frisian – Frankish wars The Frisian – Frankish wars were a series of conflicts between the Frankish Empire and the Frisian kingdom in the 7th and 8th centuries . The wars were mainly about control of the Rhine delta . But after the death of the Frisian king Redbad , the Franks gained the upper hand . In 734 at the Battle of the Boarn the Frisians were defeated and the Franks annexed the Frisian lands between the Vlie and the Lauwers . Only the Frisians east of the Lauwers remained independent . In 772 they lost their independence as well . The wars ended with the last uprising of the Frisians in 793 and the pacification of the Frisians by Charles the Great . Background . The displacements of peoples during the Migration Period resulted in the Frisian settlements in the north and the west of the Low Countries the Saxons in the east , the Warnen at the mouth of the Rhine and the Franks further south around the Scheldt . There , under the leadership of their Merovingian kings , they had an important role in the politics in northern Gaul . The Frisians consisted of loosely bonded tribes centered on war bands but without great power . In the second half of the 7th century the Frisian kingdom reached its maximum geographic development . The Frisian kings became interested in former Frankish lands ; under the leadership of the predecessors of Aldgisl they expanded their power to the heart of the Low Countries . The presence of the Warnen at the mouth of the Rhine remains unclear , but it appears they were likely crushed between the Frisians and Franks . Rhine delta control . Though the Merovingian king of the Franks Chilperic I ( 561 - 584 ) is mentioned in Frankish sources ( which ones ? ) as the " terror of the Frisians and the Suebi , " there is evidence that around 600 the Frisians were successful in a war led by their king Audulf . This allowed the Frisians to expand further south . By 630 the situation had changed . The Merovingian king Dagobert I brought the Frankish empire under one banner again and conquered the lands south of the Oude Rijn . This time they brought Christianity to the Frisian lands and built a church in Utrecht . After Dagobert died the Franks could not hold their position there , and around 650 the central river area , including Dorestad became Frisian again . The manufacturing of Frankish coins stopped and the city of Utrecht became the residence of the Frisian kings . Under the rule of King Aldgisl the Frisians came into conflict with the Frankish mayor of the palace Ebroin . This time the conflict was about the old Roman border fortifications . Aldgisl kept the Franks at a distance with his army . In 678 he welcomed the English bishop Wilfrid , who like him was not a friend of the Franks . Under the successor of Aldgisl , Redbad , the tide turned in favour of the Franks : in 690 the Franks were victorious in the battle of Dorestad under the mayor of the palace Pepin of Herstal . Though not all the consequences of this battle are clear , Dorestad became Frankish again , as did the castles of Utrecht and Fechten . It is thought that the influence of the Franks now extended from south of the Oude Rijn to the coast , but this is not entirely clear because the Frisians did not entirely lose control over the central river area . In any case there was an Archbishopric or bishopric of the Frisians founded for Willibrord and a marriage was held 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 Frankish lands . He concluded a treaty with the Frankish mayor of the palace Ragenfrid so that in 716 his armies entered Frankish territory as far as Cologne , where they were victorious in the Battle of Cologne . In this way all lands south of the Rhine became Frisian again . The army returned to the north with much war loot . Redbad made plans to invade the Frankish empire for the second time and mobilised a large army . But before he could do this he fell ill and died in the autumn of 719 . It is not certain who the successor of Redbad was . It is believed that there were troubles with the succession , because the Frankish opponent Charles Martel easily invaded Frisia and subjugated the territory . The resistance was so weak that Charles Martel not only annexed " Frisia Citerior " ( " nearer " Frisia south of the Rhine ) , but he also crossed the Rhine and annexed " farther " Frisia , to the banks of the river Vlie . The end of independent Frisia . In 733 , Charles Martel sent an army against the Frisians . The Frisian king Poppo was slain and his army pushed back to Eastergoa . The next year , Charles ferried an army across the Aelmere with a fleet that enabled him to sail up to De Boarn . The Frisians were defeated in Battle of the Boarn that followed , and their king , Poppo , was killed . The victors plundered and burned heathen sanctuaries . Charles Martel returned with much loot , and broke the power of the Frisian kings for good . The Franks annexed the Frisian lands between the Vlie and the Lauwers . Annexation of East Frisia . The Frankish king Charles the Great brought an end to the independence of the Frisians east of the Lauwers as well , expanding the Frankish Empire further to the east . The war began with a campaign against the East Frisians and was then continued against the Saxons , where the Saxon Wars would last thirty - two years . In 772 , Charles attacked the Frisians east of the Lauwers and the Saxons with a large army . He defeated them in several battles and so the last independent Frisian lands and the lands of the Saxons came into Frankish hands . Frisian uprisings . After their defeat , the Frisians rebelled against the Franks several times . Murder of Saint Boniface . The first Frisian bishop Boniface set out for Frisia in 754 with a small retinue . He baptized a great number and summoned a general meeting for confirmation at a place not far from Dokkum , between Franeker and Groningen . Instead of the converts he expected , a group of armed inhabitants appeared . The Frisian warriors were angry because he had destroyed their shrines . They slew the aged archbishop because , according to Boniface ' s hagiographer , they believed the chests he carried with him contained gold and other riches . They were dismayed when they discovered that the chest only contained the bishop ' s books . Uprising of 782 - 785 . Under the leadership of Widukind the Saxons continued to resist the Franks . In 782 the Frisians east of the Lauwers also began an uprising against the Franks . The uprising expanded to Frisian lands in the west that had been pacified earlier . This led to a en masse return to paganism by the population . Marauders burned churches and the priests , including Ludger , had to flee south . In response Charlemagne organized a new campaign in 783 to restore control , first over the Saxons and later over the Frisians . The Frisians aided Widukind against the Franks in 784 by sending him an army . It did not help much and he had to surrender in 785 and the Frisian uprising was severely repressed by the Franks . Uprising of 793 . In 793 the Frisians rebelled for the last time against Charlemagne . The reason for this was the forceful recruiting of Frisians and Saxons for the war against the Avars in the east . Under the leadership of dukes Unno and Eilrad , an uprising arose east of the Lauwers and spread to other Frisian lands . This led to a temporary return to paganism , and again priests had to flee . This uprising was also suppressed by the Franks .