Information comes from:

Calvesi, Maurizio. Treasures of the Vatican: St. Peter's Basilica: the Vatican museums and galleries, the treasure of St. Peter's, the Vatican grottoes and necropolis, the Vatican palaces. Geneva?: Skira] ;, 1962. Print.

Jodidio, Philip. Discovering architecture: how the world's great buildings were designed and built. New York: Universe Publishing, 2013. Print.

"St. Peter's Basilica." Wikipedia. Wikimedia Foundation, 9 Oct. 2013. Web. 18 Sept. 2014. <http://en.wikipedia.org/wiki/St._Peter's_Basilica>.