Little is known of the origin or history of the Raetians, who appear in the records as one of the most powerful and warlike of the Alpine tribes. Livy states distinctly that they were of Etruscan origin (a belief that was favored by Niebuhr and Mommsen). A tradition reported by Justin and Pliny the Elder affirmed that they were a portion of that people who had settled in the plains of the Po and were driven into the mountains by the invading Gauls, when they assumed the name of "Raetians" from an eponymous leader Raetus. Even if their Etruscan origin be accepted, at the time when the land became known to the Romans, Celtic tribes were already in possession of it and had amalgamated so completely with the original inhabitants that, generally speaking, the Raetians of later times may be regarded as a Celtic people, although non-Celtic tribes (es. Euganei) were settled among them.
The Raetians are first mentioned (but only incidentally) by Polybius, and little is heard of them till after the end of the Republic. There is little doubt, however, that they retained their independence until their subjugation in 15 BC by Tiberius and Drusus.
At first Raetia formed a distinct province, but towards the end of the 1st century AD Vindelicia was added to it; hence Tacitus (Germania, 41) could speak of Augusta Vindelicorum (Augsburg) as "a colony of the province of Raetia". The whole province (including Vindelicia) was at first under a military prefect, then under a procurator; it had no standing army quartered in it but relied on its own native troops and militia for protection until the 2nd century AD.
During the reign of Marcus Aurelius, Raetia was governed by the commander of the Legio III Italica, which was based in Castra Regina (Regensburg) by 179 AD. Under Diocletian, Raetia formed part of the diocese of the vicarius Italiae, and was subdivided into Raetia prima, with a praeses at Curia Raetorum (Chur) and Raetia secunda, with a praeses at Augusta Vindelicorum (Augsburg), the former corresponding to the old Raetia, the latter to Vindelicia. The boundary between them is not clearly defined, but may be stated generally as a line drawn eastwards from the lacus Brigantinus (Lake Constance) to the Oenus (River Inn).
During the last years of the Western Roman Empire, the land was in a desolate condition, but its occupation by the Ostrogoths in the time of Theodoric the Great, who placed it under a dux, to some extent revived its prosperity. Much of Raetia prima remained as a separate political unit, Raetia Curiensis, for several centuries, until it was attached to the Duchy of Swabia in AD 917.