In fact, Pope Julius II who commissioned the rebuilding of Saint Peter's (the pope before Pope Leo X) said he wanted to create the most grandiose church in all of christendom and they did the church itself Saint Peter's Basilica was tremendously important to the authority of the pope by tradition Saint Peter is buried under that church and Saint Peter was charged by Christ himself to lead the church so Saint Peter is understood to be the first pope and so every succeeding pope is taking on the job of Saint Peter from Christ himself and so the very authority of this office is vested in this building. 