This Romanesque Collegiate church of Cathedral was built in the 12C and is literally covered in frescoes inside: those by Bartolo di Fredi from Siena depict the Old Testament with a colourful yet naïve verve and are simply adorable! Opposite the life of Christ is told in another earlier series of frescoes by an illustrious unknown Barna da Siena who fell from his scaffolding on completing the work.