Aosta was settled in proto-historic times and later became a centre of the Salassi, many of whom were killed or sold into slavery by the Romans in 25 BC. The campaign was led by Marcus Terentius Varro, who then founded the Roman colony of Augusta Praetoria Salassorum, housing 3,000 retired veterans. After 11 BC Aosta became the capital of the Alpes Graies ("Grey Alps") province of the Empire. Its position at the confluence of two rivers, at the end of the Great and the Little St Bernard Pass, gave it considerable military importance, and its layout was that of a Roman military camp.
After the fall of the Western Empire, the city was conquered, in turn, by the Burgundians, the Ostrogoths, the Byzantines. The Lombards, who had annexed it to their Italian kingdom, were expelled by the Frankish Empire under Pepin the Short. Under his son, Charlemagne, Aosta acquired importance as a post on the Via Francigena, leading from Aachen to Italy. After 888 AD it was part of the renewed Kingdom of Italy under Arduin of Ivrea and Berengar of Friuli.
In the 10th century Aosta became part of the Kingdom of Burgundy. After the fall of the latter in 1032, it became part of the lands of Count Humbert I of the House of Savoy. After the creation of the county of Savoy, with its capital in Chambéry, Aosta led the unification of Italy.
Under the House of Savoy, Aosta was granted a special status that it maintained when the new Italian Republic was proclaimed in 1948
