The Chapel of St. Michael, looking west, early 11th century. The chapel is accessed via a narrow spiral staircase to the right of the narthex. It is laid out just like the narthex below, but has a much higher ceiling (12.5m) and more light. It is the strongest part of the church and looks much like a castle with its strong masonry and arrow-slit windows (the ones visible from the west front). This chapel served not only as a spiritual sanctuary but also a place of refuge and defense during invasions, which were fairly frequent in the Middle Ages.