Constructed between 1704 and 1714 but extensively damaged during WWII and subsequently rebuilt, this church was named after the King of Castile. Its ornate interior features stucco and marble decoration, as well as statues by Giovanni Baratta. The main marble altar includes Baratta's sculpture of an angel freeing two slaves and acknowledges the role of this congregation in paying the ransom for Christian slaves in North Africa during the 17th century.