The Cathedral of Santa Maria Assunta, commissioned from Rossellino by Pope Pius II, was consecrated on 29 August 1462.
The imposing travertine façade, which almost appears to be striding onto the square from the sweeping panorama of the Val d’Orcia, is in the classical architectural style of Leon Battista Alberti, its simple barnlike structure topped by a pediment with the Piccolomini papal arms set in a wreath and divided into three parts by large pilasters reflecting the church’s interior arrangement.
The nave and two side aisles in the Latin cross interior are all the same height, in the style of the Hallenkirchen that Aeneas Silvius Piccolomini had had the opportunity to admire on his travels in northern Europe. Pius II’s ideal plan, therefore, was to harmonise the Gothic tradition with the style of classical antiquity.
The aisles are separated by two rows of piers with half-columns, topped by capitals and raised stretches of trabeation supporting the ribbed vaulting. The tall aisles of the same height and the single-light windows allow such intense light to penetrate into the building that the Pope called it his “house of glass” or domus vitrea:
“when the sun beats on it”, it does so in such a way that “those inside the church feel as though they are enclosed by walls not of stone but of glass” (E.S. Piccolomini, Commentari IX,24).
The altars in the chancel area host splendid altarpieces commissioned by the Pope from the most fashionable Sienese artists of the mid-15th century, Sano di Pietro, Vecchietta, Matteo di Giovanni and Giovanni di Paolo who, while remaining loyal to the Sienese gold ground tradition, were able in this context to get to grips with the innovations of the Florentine Renaissance.
All the altarpieces share an architectural structure inspired by classical buildings and the iconography of the Virgin and Child. The Assumption of the Virgin is depicted in only one instance, in reference to the Cathedral’s dedication. In each case, the paintings highlight Pius II’s special devotion to the Blessed Virgin while also portraying saints associated with the region, with his family’s traditional names or with his own personal history.