The cathedral's interior is extremely ornate, standing in sharp contrast with the façade. The interior was largely decorated by Mattia Preti, the Calabrian artist and knight, at the height of the Baroque period. Preti designed the intricate carved stone walls and painted the vaulted ceiling and side altars with scenes from the life of John the Baptist. The figures painted into the ceiling next to each column initially appear to the viewer as three-dimensional statues, but on closer inspection we see that the artist cleverly created an illusion of three-dimensionality by his use of shadows and placement. Also noteworthy is the fact that the carving was all undertaken in-place (in-situ) rather than being carved independently and then attached to the walls (stucco). The Maltese limestone from which the Cathedral is built lends itself particularly well to such intricate carving. The whole marble floor is an entire series of tombs, housing about 400 Knights and officers of the Order. There is also a crypt containing the tombs of Grand Masters like Philippe Villiers de L'Isle-Adam, Claude de la Sengle, Jean Parisot de Valette, and Alof de Wignacourt.