The Cathedral named for the Assumption of the Virgin Mary certainly wasn't Volterra's first Duomo. Back in the 9th century, there was a pre-existing church dedicated to the Virgin Mary. Rebuilt following a violent earthquake in 1117, it was expanded in the late 13th century. The basilica's transept is classically decorated, including ornate lunettes using the flattened ornamentation technique and sloping rhombuses that once housed ceramic basins. These same rhombuses are also found on the salients of the facade, divided into three sections with large quadrangular pilaster strips in the Lombard style. The marble doorway is built using recovered materials from the Roman theatre of Vallebuona.
The interior, while maintaining in its structure and layout a Latin cross plan, has a Late Renaissance appearance. The space is divided by 22 columns covered in stucco simulating pink granite, while white stucco capitals were created in the 16th century by Leonardo Ricciarelli. The middle nave and transept are covered by a majestic coffered ceiling, a beautiful combination of geometric, decorative and floral elements as well as featuring figures of saints, two large ovals of the Assumption and the Holy Spirit, designed by Francesco Capriani, carved by Jacopo Paolini, and gilded by Fulvio Tucci between 1580 and 1584. Along the nave there are six chapels, which house works by artists from the late 16th century. In 1584 the pulpit was reassembled with 12th-century elements. The main altar contains the elegant ciborium by Mino da Fiesole (1471). At the sides, above two twisting columns dating to the 12th century, are two angels also by Mino. Behind there’s the choir screen, whose Gothic stalls were made by Sienese hands in the late 14th century. In the middle of the vault the Holy Father is depicted, a fragment of a pictorial cycle by Niccolò Circignani with Stories of the Life of the Virgin Mary. To the right of the altar, the first chapel contains the relics of Saint Octavian, in a sarcophagus made by Raffaello di Andrea Cioli da Settignano. In the adjacent chapel there’s the wooden group of the Deposition (1228), a masterpiece of Romanesque wooden sculpture. Lastly, there’s the chapel built along the sides of the cathedral, dominated by the work of Jacopo Chimenti (known as L’Empoli”) showing Saint Charles praying before the Virgin Mary. The Chapel of Our Lady of the Sorrows (Cappella dell’Addolorata) is also part of the cathedral complex. The chapel contains two statuary groups in painted terracotta, attributed to Andrea della Robbia: the Nativity, with the fresco of the Magi by Benozzo Gozzoli, and the Adoration of the Magi.