In 1794, a sundial was created by Giuseppe Piazza at the end of the central aisle at the behest of Archbishop Filippo Lopez y Royo. The Palermo University professor and astronomer had precious materials used in its construction: it consists of a prismatic brass bar, slightly raised, set into the floor and finished with a white marble edging. Holes in the bar indicate when the sun enters the various signs of the Zodiac. These are represented on the floor with polychrome marble inlays. Another element of the Cathedral’s sundial is the gnomon, made by drilling a hole in a limestone and covering it with a metal plate. It is located in the dome in front of the Chapel of San Francesco di Paola.