The walls and vaulting of the church ceiling are supported by a series of stepped buttresses along the outer walls of nave and apse. Each buttress is decorated with gargoyles and a twisted pinnacle, while the upper walls of the church have decorative crenellations. The main portal is located in the middle of the South façade and was the last feature of the façade to be built. This portal, which has remained unfinished, is prominent in relation to the façade and has several archivolts with empty niches. The tympanum is decorated with two letters "A" inserted in an "O", and a mullion divides the entrance in two smaller, twin-arched portals. The South side of the apse is decorated by a beautiful, large mullioned window with late Gothic tracery.