The collegiate church of Saints Quirico and Giulitta in San Quirico d’Orcia is an ancient parish church built towards the end of the 12th century, with a baptistery dating back to the 8th century. The oldest part is the facade, in particular the main portal, which is Lombard style with a rounded arch, decorated and supported by two pairs of sandstone columns on each side. On the architrave of the portal there are two sculpted crocodiles. In the centre of the lunette, there is a sculpted raised figure, today identified as Saint Quiricus. In the second half of the thirteenth century, works to extend the two lateral portals were carried out. The first, dated 1288, was attributed to Giovanni Pisano, who was working on the construction of the Siena Cathedral during those years. In 1644, the parish church became a Collegiate church. Between 1724 and 1733, Cardinal Anton Felice Zondadari ordered the demolition of the old bell tower, which was to be replaced, and the interior was renovated in Baroque style.
The church has a Latin cross floor plan with a single nave and apsidal chapels. To the left of the main altar, there is a large 15th century altarpiece depicting the Madonna with Child, the Angels and the Saints on a golden background, by Sano di Pietro. In the lunette, the Resurrection and the Descent of Christ into Limbo are depicted. To the left of the nave, at the entrance of the church, there is the tombstone of Prince Henry II of Nassau, who died in 1451. A beautiful nineteenth century Venetian-style organ was transferred to the collegiate church from the Abbey of Monte Oliveto in 1810.