Aosta, city, capital of Valle d’Aosta region, northwestern Italy, at the confluence of the Buthier and Dora Baltea rivers and commanding the Great and Little St. Bernard pass roads, north-northwest of Turin. It was a stronghold of the Salassi, a Celtic tribe that was subdued by the Romans in 25 bce, and a Roman town (Augusta Praetoria) was founded there by Augustus in 24 bce. A bishopric from the 5th century, the town was always the most important centre of the Valle d’Aosta; it became the regional capital in 1945. It was the birthplace of St. Anselm (1033/34–1109), archbishop of Canterbury.

Aosta retains the walls, two gates, and the street plan of its Roman predecessor, as well as a triumphal arch in honour of Augustus and remains of the theatre, the amphitheatre, and the road from Eporedia (modern Ivrea). The rectangular street plan, laid out in equal blocks (insulae), is an outstanding example of Roman formal city planning. Of later monuments, the cathedral is notable for its treasury and 12th-century floor mosaics, and the collegiate church of S. Orso for its Romanesque cloisters and Gothic choir stalls. Aosta is a commercial centre and has a metallurgical industry. Pop. (2001) 34,644.

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Valle d’Aosta, region, northwestern Italy, containing the upper basin of the Dora Baltea River, from its source near Mount Blanc to just above Ivrea. The region is enclosed on the north, west, and south by the Alps. Originally the territory of the Salassi, a Celtic tribe, the valley was annexed by the Romans; Aosta, the capital, was founded in 24 bc. After the fall of the Western Roman Empire in the 5th century, the Valle d’Aosta formed part of the Burgundian and Frankish kingdoms, passing through many hands until it was acquired in the 11th century by the House of Savoy (the future royal house of Italy). Aosta province was formed from part of Torino province in 1927, and the autonomous region of Valle d’Aosta was created in 1945 in recognition of the special French linguistic and cultural orientation of the area. At that time, the southern portion was returned to Torino province.

The busy highway from the Po Valley to the Great and Little St. Bernard passes runs through the region, which is important for dairy products and tourism and has hydroelectric resources. There is some industry in the area. A nationalist group supporting increased use of French in the region gained political and electoral strength throughout the 1970s. Area 1,259 square miles (3,262 square km). Pop. (2006 est.) 123,978.

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