In June 1158 Frederick set out upon his second Italian expedition, which was signalized by the establishment of imperial officers called _podestas_ in the cities of northern Italy, the revolt and capture of Milan, and the beginning of the long struggle with pope Alexander III., who excommunicated the emperor on the 2nd of March 1160. During this visit Frederick summoned the doctors of Bologna to the diet held near Roncaglia in November 1158, and as a result of their inquiries into the rights belonging to the kingdom of Italy he obtained a large amount of wealth. Returning to Germany towards the close of 1162, Frederick prevented a conflict between Henry the Lion, duke of Saxony, and a number of neighbouring princes, and severely punished the citizens of Mainz for their rebellion against Archbishop Arnold. A further visit to Italy in 1163 saw his plans for the conquest of Sicily checked by the formation of a powerful league against him, brought together mainly by the exactions of the _podestas_ and the enforcement of the rights declared by the doctors of Bologna. Frederick had supported an anti-pope Victor IV. against Alexander, and on Victor's death in 1163 a new anti-pope called Paschal III. was chosen to succeed him. Having tried in vain to secure the general recognition of Victor and Paschal in Europe, the emperor held a diet at Wuerzburg in May 1165; and by taking an oath, followed by many of the clergy and nobles, to remain true to Paschal and his successors, brought about a schism in the German church. A temporary alliance with Henry II., king of England, the magnificent celebration of the canonization of Charlemagne at Aix-la-Chapelle, and the restoration of peace in the Rhineland, occupied Frederick's attention until October 1166, when he made his fourth journey to Italy. Having captured Ancona, he marched to Rome, stormed the Leonine city, and procured the enthronement of Paschal, and the coronation of his wife Beatrix; but his victorious career was stopped by the sudden outbreak of a pestilence which destroyed the German army and drove the emperor as a fugitive to Germany, where he remained for the ensuing six years. Henry the Lion was again saved from a threatening combination; conflicting claims to various bishoprics were decided; and the imperial authority was asserted over Bohemia, Poland and Hungary. Friendly relations were entered into with the emperor Manuel, and attempts made to come to a better understanding with Henry II., king of England, and Louis VII., king of France.