The cathedral of Santa Maria Assunta, designed by Rossellino by order of Pius II, was consecrated in 1462. The imposing travertine façade, which almost seems to advance on the square from the vast panorama of the Val d’Orcia, reflects the classical canons of architecture by Leon Battista Alberti.
The interior, in the shape of a Latin cross, presents all the aisles of the same height, according to the Hallenkirchen model, which Enea Silvio Piccolomini had had the opportunity to admire while traveling in Northern Europe. The interior is enriched by altarpieces commissioned by the Pope to the Sienese artists most in vogue in the mid-fifteenth century.
The light, which from the Val d’Orcia enters through the windows of the apse “when the sun beats”, means that “those who are inside the church have the feeling of being inside glass walls instead of stone walls ”(ES Piccolomini, Commentarii).