The current church is constructed on the site of the old parish church which we hear about until the end of the 8th century. The Collegiate church is designed according to a Latin cross plan with a single nave and has three external doors. The first, built in sandstone and travertine from Bagno Vignoni, inside its large arch contains an extraordinary wealth of symbolic and religious imagery. One of the two lateral doors has been attribtued to Giovanni Pisan who in those years (1287-1288) was employed at Siena working on the construction of the Cathedral. The bell tower, as it appears today, was constructed at the end of the 18th century. The high altar in the Rococo style was commissed in 1724 by the Cardinal Flavio Chigi to Lombard artists. Behind the high altar is the backbone of the choir, one of the more interesting works in San Quirico: inlaid by the Sienese Antonio Barili between 1482 and 1502 for the Cathedral of Siena, they were acquired by the Marquis Chigi and placed in the choir of the Collegiate in 1749.