The Frisii were an ancient tribe, who were neighbours of the Roman empire in the low-lying coastal region between the Rhine and the Ems rivers, in what what is now the northern Netherlands. They are not mentioned in Roman records after the third century, and archaeological records show that there was population decline, and frequent flooding caused by sea level rise. It is probable that many Frisii were among the early "Saxons" who settled in Britain. They are nevertheless also likely to be ancestors of the Frisians of today, whose material culture can be traced back to new settlements in the early Middle Ages.
Before the entry of the Romans into the area, settlers started to colonize the area in newly formed marshlands in the 6th or 5th centuries BC. 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 Chauci, east of the Ems.