↑ The Geography of Power:Matilda of Tuscany and the Strategy of Active Defense, Valerie Eads, Crusaders, Condottieri, and Cannon: Medieval Warfare in Societies Around the Mediterranean, ed. Donald Joseph Kagay and L. J. Andrew Villalon, (Brill, 2003), 358.
↑ The Reform of the Church, J.P. Whitney, The Cambridge Medieval History, Vol. V, (Cambridge University Press, 1968), p. 23.
↑ The Reform of the Church, J.P. Whitney, The Cambridge Medieval History, Vol. V, (Cambridge University Press, 1968), p. 31.
