The sanctuary is entered through three rectangular portals, the central one being wider and separated by a pair of porphyry columns with gilded Composite capitals. These support an entablature with Cosmatesque mosaic work on its architrave and a gilded epigraph on its frieze reading "There is not a holier place in all the world". The walls of the sanctuary are revetted with marble slabs of the same sort as the nave, except for two porphyry ones behind the altar. Below the Papal altar, protected by an enormous wrought iron cage, lie two bronze doors, covered with reliefs and inscriptions dating from the 13th century. These decorations cover the cypress wood ark, specifically made by Leo III to contain the illustrious treasures and relics.