Sondrio (Sundrium, Sondrio, Lombard: Sùndri, Sunder) is an Italian town and comune located in the heart of the Valtellina. Sondrio counts approximately 22,600 inhabitants and it is the administrative centre for the Lombard Province of Sondrio.
The area of Sondrio was populated in ancient times by the Ligures and, from the 5th century BC, by the Celts. 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 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.
Another important piece of Sondrio's economy is its banking industry, with the Banca Popolare di Sondrio and the Credito Valtellinese both headquartered in Sondrio and listed on the Milan Stock Exchange.