Founded in the 4C and rebuilt in the 12C, the Basilica di San Clemente is one of Rome's earliest basilicas. In the upper basilica, note the magnificent mosaic in the apse and the frescoes in the chapel dedicated to St Catherine. In the lower basilica, the nave is decorated with frescoes on which some of the characters are accompanied by phrases written in a language halfway between Latin and vernacular Italian. Beneath the basilica, a house dating from the 1C was later converted into a mithraeum (temple to Mithras).