Back in 507AD King Clovis converted to Christianity and decided to build a basilica on the very site where The Pantheon stands today and Saint Genevieve, who was the patron saint of Paris that protected the city from the barbarians, was buried in this basilica in 512AD. This meant that the basilica and further churches were dedicated to Saint Genevieve and in 1744 after King Louis XV had been seriously ill, he attributed his recovery to the prayers of Saint Genevieve and decided that he would have a prestigious church built on the same spot as the original basilica dedicated to her. So, in 1755 the design for the new basilica was entrusted to Jacques-Germain Soufflot, the chief architect of King Louis, and the overall design was that of a Greek cross with a very impressive portico of Corinthian columns, but the then Basilica has a combination of different styles like Greek architecture and also a Gothic system that utilised flying buttresses and arches to make it as light as possible
