The impressive Diocletian's Palace substructure halls are among the best preserved parts of the palace / UNESCO heritage. Different in shapes and sizes the substructure halls were built to level the southern residential part with the rest of the palace. They therefore had the same layout as the emperor's chambers above them. Over time, they were completely buried, and the old citizens of Split believed that they were prisons where Christians had been tortured. The excavations in the 19th century discovered their real purpose and archaeological value. Today the central hallway connects Riva with the Peristyle, and the western part of the substructure halls, which is almost entirely preserved, is where the most attractive exhibitions and events take place.