The Cathedral of Mazara del Vallo dominates the Piazza della Repubblica and is a monument to the town's long and mixed history. Founded by Roger I in 1093 on the site of a mosque — itself built on an earlier Byzantine church — it was rebuilt in Baroque style in the 17th and 18th centuries.
The interior has a number of notable artworks, including a relief of Roger I on horseback trampling a Saracen, a provocative image from the Norman period. The Baroque facade is well-proportioned and the piazza in front is one of the more pleasant open spaces in western Sicily. The cathedral is also the seat of the Diocese of Mazara del Vallo, which covers a large area of western Sicily.