It was thus necessary for him to reconcile with the pope. In a
             Treaty in 1153 with Pope Eugene III, Frederick promised to assist him against Arnold of Brescia and against the powerful Normans in Sicily. Frederick entered Italy in 1154 and was crowned in Rome on June 18, 1155. The reluctance of his troops to remain in Italy forced him to return to Germany without assisting the new pope, Adrian IV, against King William I of Sicily. Adrian, allied himself with William in 1156, turned against Frederick. At the Diet of Besançon in 1157 the papal legate presented a letter that Frederick interpreted as a claim by the pope that the empire was a papal fief. Frederick replied that he held the throne "through the election of the princes from God alone" and prepared to invade Italy, where Milan had begun the conquest of Lombardy. Adrian explained that he had not intended that interpretation of his words, but Frederick entered Italy, seized Milan, and at the Diet of Roncaglia in 1158 laid claim, as emperor and king of the Lombard's, to all imperial rights, including the appointment of an imperial governor, in every town.
             The heavy handedness of his German officials led to the revolt of Milan, Brescia, Crema, and their allies, in 1159. The revolt was secretly encouraged by Adrian IV. After a long siege, Frederick stormed and burned Milan in 1162. He also set up an antipope to
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