In the first years of the 19th century, the King of Naples was Murat (Napoleon's brother-in-law). He planned the square and building as a tribute to the emperor. When Napoleon was finally dispatched, the Bourbons were restored to the throne of Naples.
Ferdinand I continued the construction but converted the finished product into the church one sees today. He dedicated it to Saint Francis of Paola, who had stayed in a monastery on this site in the 16th century. The church is reminiscent of the Pantheon in Rome. The façade is fronted by a portico resting on six columns and two Ionic pillars. Inside, the church is circular with two side chapels. The dome is 53 metres high." (Text from Wikipedia).