This dominion was ruled by kings and emerged in the mid-7th century and probably ended with the Battle of the Boarn in 734 when the Frisians were defeated by the Frankish Empire.

Possibly, Frisia consisted of multiple petty kingdoms, which transformed in time of war to a unit to resist invading powers, and then headed by an elected leader, the primus inter pares.

In the Germanic pre-Migration Period (i.e., before c. AD 300) the Frisii and the related Chauci, Saxons, and Angles inhabited the Continental European coast from the Zuyder Zee to south Jutland.

[7][8][9] In the 6th century, Frisia received an influx of new settlers, mostly Angles, Saxons, and Jutes, who would come to be known as "Frisians" even though they were not necessarily descended from the ancient Frisii.

Under the rule of the king Aldgisl, the Frisians came in conflict with the Frankish mayor of the palace Ebroin, over the old Roman border fortifications.

While Aldgisl[19] 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.

[21] 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.

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,[23][24][25] and a marriage was arranged between Grimoald the Younger the oldest son of Pepin, and Thiadsvind, the daughter of Redbad, in 711.

Outside of Cologne, held by Plectrude, an ill-prepared Charles Martel was defeated by Redbad, and forced to flee to the mountains of the Eifel.

Many Austrasians, under attack by Neustrians, Frisians, and Saxons in the northeast likely rallied behind Martel because he was the only surviving adult male of the Pippinnid family.

[27] His forces then attacked the army of Chilperic II and his allies at the Battle of Amblève near Amel as they returned triumphantly from Cologne.

They spent a year together attempting to convert the Frisians to Christianity, but their efforts were frustrated when Redbad retook possession of Frisia, burning churches and killing many missionaries.

It is believed that there were troubles with the succession, because the Frankish opponent Charles Martel could easily invade Frisia and subjugate the land.

[31] The inhabitants gave hostages, converted to Christianity and recognised Frankish overlordship, but after Charles left they were punished by their fellow Frisians.

[31] Charles and Poppo's armies met on the banks of the river Boarn, perhaps at Oldeboorne, one of the Frisians' chief commercial centers at the time.

Charles ordered pagan shrines and sanctuaries to be destroyed and carried back to Francia "a great mass of spoils" (magna spolia et praeda).

In 752/753 Boniface wrote a letter to Pope Stephen II, in which it is said that Willibrord destroyed the Frisian pagan sanctuaries and temples.

[35] In the second text passage Willibord arrived on an island called Fositesland (possibly Heligoland) where a pagan god named Fosite was worshipped.

He defeated them in several battles and so brought an end to the Frisian independence, expanding the Frankish Empire further to the east, where the Saxon Wars would begin.

This led to an en masse return to paganism by the population, marauders burned churches and the priests had to flee south.

They laid Frisia under the rule of grewan, a title that has been loosely related to count in its early sense of "governor" rather than "feudal overlord".

During this time Charlemagne imposed the Lex Frisionum, a penal code which stratified Frisia into Nobility, Freemen, Serfs and Slaves.

The Danish king though was shortly after the invasion killed by one of his own men, and his fleet withdrew to Denmark before it came to any clash with regular Frankish forces.