Walter Ullmann 
Growth of Papal Government in the Middle Ages [PDF ebook] 

This book reveals how the medieval papacy grew from modest beginnings into an impressive institution in the Middle Ages and deals with a wide field. It charts the history of the papacy and its relations to East and West from the 4th to the 12th centuries, embraces such varied subjects as law, finance, diplomacy, liturgy, and theology. The development of medieval symbolism is also discussed as are the view of eminent political scientists of the period. This re-issues reprints the revised, 3rd edition of 1970.