Frisii

The Frisii were an ancient tribe, living in the low-lying region between the Rhine–Meuse–Scheldt delta and the River Ems, sharing some cultural and linguistic elements with the neighbouring Celts. The newly formed marshlands were largely uninhabitated until the 6th or 5th centuries BC, when inland settlers started to colonize the area. As sea levels rose and flooding risks increased, the inhabitants learned to build their houses on village mounds or terps. The way of life and material culture of the Frisii hardly distinguished itself from the customs of the Chaucian tribes living farther east. The latter, however, were considered to be part of the Germanic tribal confederation.

During the 1st century BC, Romans took control of the Rhine delta but Frisii to the north of the river managed to maintain some level of independence. There was a lot of interaction, however, as Frisian and Chaucian mercenary bands enlisted in the Roman army and Roman traders established themselves north of the limes. There may have been Roman military outposts on Frisian territory. Some or all of the Frisii may have merged with Frankish and Saxon migrants in late Roman times, but they would retain a separate identity in Roman eyes until at least 296, when Frisian, Frankisch and Chamavi groups were forcibly resettled as laeti. Archaeological findings suggest that they may have been transported to Flanders and Southwestern England.

The area where the original Frisii lived, was largely deserted during the Migration Period, probably due to political instability and piracy, as well as climatic deterioration and frequent flooding caused by sea level rise. When changing environmental and political conditions made the region attractive again it was repopulated in the 5th century by Anglo-Saxon settlers from Northwestern Germany and Southwestern Denmark, who adopted the old name Frisii. These new 'Frisians' lived in the coastal fringe stretching roughly from present-day Bruges to Bremen, including many of the smaller offshore islands. They incorporated the remainer of indigenous groups that lived in the area and successfully conquered what would become their new homelands. Medieval and later accounts of 'Frisians' refer to these 'new Frisians' rather than to the ancient Frisii.