Formerly an Ancient Roman military camp, today's Sondrio was founded by the Lombards: in their language Sundrium meant "Exclusive property", referring to the status of free men (arimanni) of the holders of the city and the surrounding land.
After the fall of the Lombard Kingdom in Italy, Sondrio became part of the Holy Roman Empire. The Capitanei of Vizzola, who controlled much of the Valtellina, had it in 1040 from the emperor Henry II. From 1310 to 1335 the city was involved in the war between the Guelph and Ghibelline factions of the nearby Como, and its war against Milan. After having resisted several attacks by the Comaschi, in 1335 Sondrio and Valtellina became part of the Visconti Milanese dominions.
From the second half of the 16th century to the end of the 18th century, Sondrio was governed by the Tre Leghe Grigie ("Three Grey Leagues") of the Grisons, as the capital city of Valtellina. After the Reformation, Sondrio was the centre of heavy struggles between the Catholic Valtellinesi and the Protestant Grisons. In 1620 the citizens, led by Giacomo Robustelli, killed 180 Protestants and declared the independence of the Valtellina.
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The territory of Sondrio has numerous vineyards; wines produced include the Sassella and Grumello. Wine represents one of the main resources of this region, together with tourism, especially in winter.
The heart of Sondrio is its central Garibaldi Square. Not far from it is the Palazzo Sassi, home of the Art and History Museum of Valtellina. In a dominant position, near the ancient road to the Valmalenco, linking the town to Switzerland, stands the Masegra Castle, housing the Historical Museum of the Grisons Domination.
The church of Santi Gervasio e Protasio rebuilt in Neoclassical-style in 1838, was built in the 12th century as a Romanesque pieve and collegiate church. Other sights include the Torre Ligariana, once the collegiate's bell tower, and the Palazzo Pretorio, once the seat of the Grisons government.
Across the railway in direction of Milan there is the ancient Church of Maria della Sassella,[5] which the local tradition dates back to the 10th century.[6][7] In March 2021 the Roman Catholic Diocese of Como declared the church to be a diocesan Marian sanctuary.[8]