Knapke, P. J. (1939). Frederick Barbarossa's conflict with the papacy: A problem of church and state. Catholic University of America.
Chicago-Zitierstil (17. Ausg.)Knapke, Paul Justin. Frederick Barbarossa's Conflict with the Papacy: A Problem of Church and State. Washington: Catholic University of America, 1939.
MLA-Zitierstil (9. Ausg.)Knapke, Paul Justin. Frederick Barbarossa's Conflict with the Papacy: A Problem of Church and State. Catholic University of America, 1939.
Achtung: Diese Zitate sind unter Umständen nicht zu 100% korrekt.