This curious basilica in Romanesque and Gothic style, now a UNESCO World Heritage Site, was originally built as part of a Benedictine monastery. Finished in 1260, the basilica was altered in the 18C, when it was decorated in Baroque style, notably with the addition of its two towers. It was only in 1884 that its most precious feature was discovered, namely a group of frescoes illustrating the life of St John which date from the second half of the 13C.