The Church of Jesus or Casa Professa was built on a site traditionally considered a refuge for hermits. The large construction was designed by the Jesuit architect Giovanni Tristano and was originally composed of just one central nave. At the beginning of 1600, the walls dividing the chapels were removed creating three naves. The design of the interior is an important example of a fusion between architecture, painting and plaster decoration. The mischio decoration (fine marble inlaid with flowers or figures) is particularly lively. At the back of the church there is an artistic monumental complex made up of a magnificent sacristy, a small museum, underground crypts, and an oratory on the second floor. This oratory, L'Oratorio del Sabato (the Oratory of Saturday) which belonged to the Jesuit community is dedicated to the Cross and Martyrdom of Christ; it is a baroque hall that was decorated in 1740 with stuccos by Procopio Serpotta and it also had large paintings on the side walls that were removed years ago. A wonderful wooden crucifix of 1600, the fresco of the vault describing the coronation of the Virgin and a small portrait of the Virgin are the real jewels here.