^Panofsky, Erwin. "The First Two Projects of Michelangelo's Tomb of Julius II". The Art Bulletin, Volume 19, No. 4, December 1937. pp. 561–579.
^Fly, Richard. Shakespeare's Mediated World. Amherst, MA: University of Massachusetts Press, 1976. p. 30.
^Charles Robertson, "Allegory and Ambiguity in Michelangelo's Slave", in The Slave in European Art: From Renaissance Trophy to Abolitionist Emblem, ed. Elizabeth McGrath and Jean Michel Massing, London (The Warburg Institute) 2012.