The chapel existed before the cathedral took shape in the 12th century. From the 14th century, it was heavily modified and decorated with frescoes. The relics of Saint-Rieul de Senlis, famous evangelizer of the region and first bishop of Senlis in the 4th century, are treasured in the chapel. The space also serves as sacristy and worship space. Discover the pre-Romanesque chapel on the occasion of these European Heritage Days.