Like the other Franks in this period, the Salian Franks were a Germanic people living near the river Rhine, which had long been a militarized border. The Salians, unlike other Franks, first appear living inside the Roman Empire, living in the Rhine delta in the modern Netherlands. In modern works they are frequently contrasted with their neighbours to the east, known as the Rhineland or Ripuarian Franks, who eventually held the Roman city of Cologne, in modern Germany. Exactly how the Franks in these areas were politically connected or separated, and how many groups there were, is unknown until the time when they all fell under the reign of Clovis I. A much later author, Gregory of Tours, said that in old records he found it seemed the Franks had once had kinglets (reguli) in each city they held.
Although often treated as a tribe it has also been argued by Matthias Springer that this might represent a misunderstanding. All of the classical mentions of them seem to derive from one mention by Ammianus Marcellinus of "Franks, those namely whom custom calls the Salii". Ammianus, who served in the Roman military, reported that the Salii were pushed from their home in Batavia, into Toxandria (both within the empire), by the non-Roman Chamavi. The first historian to say that the Salians had been pushed into the empire from outside was Zosimus, but his description of events seems to be confused and derived from others.
The account of Zosimus, that the Salians had been pushed into the empire as a single tribe, is still often accepted. In this case, their homeland may have been between the Rhine and the IJssel in the modern day Dutch region of the Veluwe, Gelderland, and they may have given their name to the region of Salland. It has also been proposed that the Salii might have been one of the peoples making up the large nation of the Chauci during the Roman empire, most of whom apparently became Saxons. (The difference between Saxons and Franks in the earliest records which mention them is not clear.)
In 358, the Salians came to some form of agreement with the Romans, which allowed them to stay keep settlements south of the delta in Toxandria, between the rivers Scheldt, Maas, and Demer, roughly the area of the current Dutch province of Noord-Brabant, and adjacent parts of the two bordering Belgian provinces of Antwerpen and Belgian Limburg, the so-called "Kempen".
The later Merovingian kings responsible for the conquest of Gaul are thought to have had Salian ancestry, because they applied so-called Salian law (Lex Salica) in their Roman-populated territories between the Loire and Silva Carbonaria, although they also clearly had connections with the Rhineland or Ripuarian Franks even before they conquered them. The Lex Ripuaria originated about 630 and has been described as a later development of the Frankish laws known from Lex Salica. On the other hand, following the interpretation of Springer the Lex Salica may simply have meant something like "Common Law".