 The Bishop of Rome tried to extend his territory from the city of Rome to the whole of Italy and further to the whole of the Western Roman Empire (in accordance with the Donation of Constantine).The coronation of Charlemagne in the year 800, which began the Carolingian Empire, marked the appearance of a secular authority with universal claims.The two century long coexistence of the Pontiff and the Empire (regnum et sacerdocium) was difficult and yielded the Investiture Controversy and several different ideological formulations (the theory of the two swords, Plenitutdo postestatis, "Dictatus papae", condemnations of simony, and nicolaism).