San Quirico d'Orcia is a comune (municipality) of about 2,500 inhabitants in the Province of Siena in the Italian region Tuscany, located about 80 kilometres (50 mi) southeast of Florence and about 35 kilometres (22 mi) southeast of Siena inside the Valdorcia landscape.

The frazione of Vignoni houses a castle, a residence of the Salimbeni family in the 12th century.

It includes a top-less tower and a Romanesque church, once housing a crufix by Giambologna, now in the Museum of Montalcino.

Annexed is also the (rebuilt) 15th century Palazzo degli Amerighi, where a plot was set against the Spanish who menaced Siena in 1558–59.

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