To commemorate their victory against Florence in the Monteaperti Battle of 1260, the Sienese decided to dedicate their city to the Virgin and build a cathedral in her honor. The plan selected for the building was a traditional Latin cross with square apse and hexagonal crossing (where the nave and transept meet), its elevation comprised of a nave arcade supported by compound piers (piers with columns attached to them) and a clerestory. The black and white stripes of marble in both the cathedral's interior and exterior were specifically chosen to reference the founding of Siena by Senius and Aschius, sons of Remus, who, according to legend, were protected on their journey there by a white cloud at day-time and a black cloud at night. Called the balzana, this black and white motif is part of the city's heraldic device, confirming that in Renaissance Siena faith and politics were intertwined.
The façade, built and decorated with statuary by Giovanni Pisano in 1285-1295, features a triple entrance crowned by gabled arches to symbolize the Holy Trinity (in its present form, only the lower portion of the façade is by Giovanni). Above is a gallery, rose window, and three gables, decorated with mosaics of the Nativity, Coronation of the Virgin, and her presentation to the temple. The façade sculptures include representations of the ancient philosophers Plato and Aristotle, the prophet Habakkuk, a sibyl,kings David and Solomon, and Moses. Most have been heavily restored and are now housed in the Museo dell' Opera del Duomo in Siena, making it difficult to reconstruct their original location and placement order.
In 1265-1268, Giovanni's father, Nicola Pisano, contributed his pulpit for the cathedral's interior. Then, in the 14th century, a number of altarpieces were commissioned for its decoration. In 1308-1311, Duccio painted the main altarpiece, the Maestà (Siena, Museo dell' Opera del Duomo). Then in the decades of the 1330s and 1340s, Simone Martini contributed his Annunciation (1333; Florence, Uffizi), Pietro Lorenzetti his Birth of the Virgin (1342; Siena, Museo dell' Opera del Duomo), and his brother Ambrogio Lorenzetti the Presentation in the Temple (1342; Florence, Uffizi). The Cathedral of Siena stands as one of the great monuments of the Italian Late Gothic era and reflects the civic pride of the Sienese and their devotion to the Virgin.
Historical dictionary of Renaissance art. Lilian H. Zirpolo. 2008.