Modern scholars of the Migration Period are in agreement that the Frankish identity emerged at the first half of the 3rd century out of various earlier, smaller Germanic groups, including the Salii, Sicambri, Chamavi, Bructeri, Chatti, Chattuarii, Ampsivarii, Tencteri, Ubii, Batavi and the Tungri, who inhabited the lower and middle Rhine valley between the Zuyder Zee and the river Lahn and extended eastwards as far as the Weser, but were the most densely settled around the IJssel and between the Lippe and the Sieg. The Frankish confederation probably began to coalesce in the 210s.

The Franks eventually were divided into two groups: the Ripuarian Franks (Latin: Ripuari), who were the Franks that lived along the middle-Rhine River during the Roman Era, and the Salian Franks, who were the Franks that originated in the area of the Netherlands.

Franks appear in Roman texts as both allies and enemies (laeti and dediticii). By about 320, the Franks had the region of the Scheldt river (present day west Flanders and southwest Netherlands) under control, and were raiding the Channel, disrupting transportation to Britain. Roman forces pacified the region, but did not expel the Franks, who continued to be feared as pirates along the shores at least until the time of Julian the Apostate (358), when Salian Franks were allowed to settle as foederati in Toxandria, according to Ammianus Marcellinus.