The Baptistery of San Giovanni an octagonal 13th century religious building standing just in front of the Duomo of Volterra, in the center of the city. It was supposedly set up in the seventh century at the site of a Roman Temple dedicated to Sun worship.

Only one of the sides has been furnished with green and white marble. The Romanesque Portal has been attributed to a follower of Nicola Pisano. The 16th-century altar inside has been assigned to Balsimelli da Settignano, using a design by Mino da Fiesole. It has a painting (partially damaged during World War Two of the Assumption of the Virgin by Niccolò Circignani. Beside that altar is a marble font (1502) is by Andrea Sansovino. The Ciborium (1471) was completed by Mino da Fiesole. The Baptismal font (1759) by Giovanni Vaccà. Above it rises a statue of St John the Baptist (1771) by Giovanni Antonio Cybei. The holy water receptacle is an ancient Roman sarcophagus.