A rare and precious vestige of the Carolingian period, this oratory is considered one of the oldest churches in France. The original building was erected in the 9C on a Greek cross plan. From that period, all that remains is the eastern apse, where the treasure of the place is displayed on the vault: a remarkable mosaic, executed around 806 and composed of 130 000 assembled glass cubes. There are Byzantine, Umayyad and Mozarabic influences. A pure masterpiece.