Kampers, Franz (1909): «Frederick II», i: Catholic Encyclopedia. 6. New York: Robert Appleton Company.
Ott, Michael (1908): Conrad of Urach, Catholic Encyclopedia. 4. New York: Robert Appleton Company.
Holland, Arthur William (1911): «Frederick II, Roman Emperor», i: Chisholm, Hugh, red.: Encyclopædia Britannica. 11. (11. utg.), Cambridge University Press; s. 46–49.
Ott, Michael (1909): «Pope Gregory IX», Catholic Encyclopedia. 6. New York: Robert Appleton Company.
Hunt, William (1891): «Henry III», Dictionary of National Biography. 26. London; s. 12–31.
Rhodes, Walter Eustace (1896): «Peter des Roches», Dictionary of National Biography. 45. London; s. 52–56.
wisc.edu
images.library.wisc.edu
Van Cleve, Thomas C. (1969): «The Fifth Crusade»' (PDF), A History of the Crusades, (Setton), bind II; kapitel XI; s. 425–428
