Frisia has changed dramatically over time, both through floods and through a change in identity. It is part of the Nordwestblock which is a hypothetical historic region linked by language and culture.
The Frisii began settling in Frisia around 500 BC. According to Pliny the Younger, in Roman times, the Frisians (or, as it may be, their close neighbours, the Chauci) lived on terps, man-made hills. According to other sources, the Frisians lived along a broader expanse of the North Sea (or "Frisian Sea") coast.
Frisia at this time comprised the present provinces of Friesland and North Holland.
Frisians appear to have been among the Germanic groups who invaded Britain during the so-called Migration period (Völkerwanderung), as Angles and Saxons travelled from their home base through Frisian territory in what is now northern Germany and central Netherlands.
The 8th-century historian Bede also used the term 'Frisians' for Franks in the south of Frisia. East Anglian sources called the inhabitants of 'Frisia' Warnii instead of Frisians. In the 7th and 8th centuries, the Frankish chronologies mention this area as the kingdom of the Frisians. However, these were probably not the Frisians of Roman times. This kingdom comprised the coastal provinces of the Netherlands and the German North Sea coast. During this time, the Frisian language was spoken along the entire southern North Sea coast and, today, this region is sometimes referred to as Greater Frisia or Frisia Magna. The 7th-century Frisian realm (650-734) under the kings Aldegisel and Redbad, had its centre of power in the city Utrecht. Its end came in 734 at the Battle of the Boarn, when the Frisians were defeated by the Franks, who then conquered the western part up to the Lauwers. They conquered the area east of the Lauwers in 785, when Charlemagne defeated Widukind. This Frisia Magna was partly occupied by Vikings in the 840s, until they were expelled between 885 and 920. It has also been suggested that the Vikings did not conquer Frisia, but settled in certain parts (such as the island of Wieringen), where they built simple forts and cooperated and traded with the native Frisians. One of their leaders was Rorik of Dorestad.