The Franks (Franci or gens Francorum; Francs) were originally a Germanic people who lived near the Lower Rhine, on the northern frontier of the late Roman Empire, but they successfully expanded their power and influence during the Middle Ages, until much of the population of western Europe, particularly in or near France, were commonly described as Franks, for example in the context of their joint efforts during the crusades starting in the 11th century. This expansion came about because the romanized Frankish dynasties based within the collapsing Western Roman Empire first became the rulers of the whole region between the rivers Loire and Rhine, and then subsequently imposed power over many other post-Roman kingdoms both inside and outside the old empire.
Although the Frankish name does not appear until the 3rd century, at least some of the original Frankish tribes had long been known to the Romans under their own names, both as allies providing soldiers, and as enemies. The Franks were first reported as working together to raid Roman territory. However, from the beginning, the Franks also suffered attacks upon them from outside their frontier area, by the Saxons, for example, and as frontier tribes they desired to move into Roman territory, with which they had centuries of close contact. Frankish peoples subsequently living inside Rome's frontier on the Rhine river are often divided by historians into two groups - the Salian Franks to the west, who came south via the Rhine delta; and the Ripuarian or Rhineland Franks to the east, who eventually conquered the Roman frontier city of Cologne and took control of the left bank of the Lower Rhine in that region.
In the middle of the 5th century, Childeric I, a Salian Frank, was one of several military leaders commanding Roman forces with various ethnic affiliations in the northern part of Roman Gaul, which corresponds roughly with modern France and the Low countries.