Kaiser Friedrich II.

by Winkelmann, Eduard, 1838-1896
Darmstadt, Wissenschaftliche Buchgesellschaft, 1967
(Unveränderter reprografischer Nachdruck der Ausg. Leipzig 1889-1897.).

Frederick the Second, 1194-1250.

by Kantorowicz, Ernst H. (Ernst Hartwig), 1895-1963
New York, F. Ungar Pub. Co. 1957

The infidel emperor and his struggles against the pope; a chronicle of the thirteenth century,

by Wiegler, Paul, 1878-1949
London, G. Routledge, 1930