Dedicated from its earliest days as a Roman Catholic Marian church, and now dedicated to the Assumption of Mary. It was the episcopal seat of the Diocese of Siena, and from the 15th century that of the Archdiocese of Siena. It is now the seat of the Archdiocese of Siena-Colle di Val d’Elsa-Montalcino.
The cathedral was designed and completed between 1215 and 1263 on the site of an earlier structure. It has the form of a Latin cross. The dome was completed in 1264. The lantern atop the dome was added by Gian Lorenzo Bernini. The bell tower has six bells, where the oldest one was cast in 1149.
The exterior and interior are constructed of white and greenish-black. Black and white are the symbolic colors of Siena, etiologically linked to black and white horses of the legendary city’s founders, Senius and Aschius. There are thirty-five statues of prophets and patriarchs grouped around the virgin. The finest Italy artists, during that time, completed works in the Cathedral. These artists were Nicola and Giovanni Pisano, Donatello, Pinturicchio, Lorenzo Ghiberti, and Bernini.