Misfortunes followed Frederick’s fresh intervention in Italy. On his way he concluded, at Augsburg, a treaty (October 1184), which ranks as the greatest of his diplomatic triumphs. In 1169 his eldest son, Henry, had been crowned King of the Romans at Aachen, when still a child. He was now becoming his father’s active fellow-worker. By the Treaty of Augsburg it was arranged that the young king should marry Constance of Sicily, the daughter of King Roger, and the aunt and heiress of the childless William II. From this sprang the ultimate union of the Hohenstaufen with the Sicilian royal house, and the conversion of southern Italy, hitherto the chiefest strength of the papal power, into the strongest bulwark of the Swabian Empire. Nor was this Frederick’s only success in Italy. [Sidenote: Revival of Frederick’s power in Italy.] The league of northern cities had broken asunder after the fear of his strong hand was removed. In 1181 the former imperialist towns—Cremona, Pavia, Lodi, Bergamo, Como—separated themselves from the confederation, and formed a league, bitterly opposed to Milan and her allies. Frederick also took advantage of the feuds of Tuscany and Bologna to build up a party there, and by lavish grants to Pisa and Lucca he secured, though at vast cost, powerful friends in middle Italy. [Sidenote: The Lateran Council, 1179. Death of Alexander III., 1181.] The Papacy had lost the great man who had so long upheld its fortunes. Alexander III.’s last important act was the assembling, in March 1179, of the third General Council of the Lateran, where the law was promulgated that a valid election to the Papacy required the votes of two-thirds of the cardinals present in the conclave. He died on 30th August 1181, full of years and honours. His five immediate successors did not reign long enough to make any real mark, and were much hampered by their strife with the Romans. Lucius III. (1181–1185) the first of the series, was still Pope when Frederick paid his sixth visit to Italy. [Sidenote: Lucius III., 1181–1185.] In November 1184 Pope and Emperor met at Verona, where Lucius refused to consent to Frederick’s proposal that his son, the young King Henry, should be crowned Emperor during his own lifetime. Under Urban III. (1185–1187), Lucius’ successor, a new quarrel between Pope and Emperor seemed imminent. [Sidenote: Urban III., 1185–1187.] The immediate pretext of this was a double election to the Archbishopric of Trier, where the imperialist choice of Rudolf of Wied had been opposed by the appointment of the ambitious Archdeacon Folmar by the hierarchical party. Urban III. consecrated Folmar archbishop, and a powerful coalition against Frederick was formed, including besides Folmar, Philip, Archbishop of Cologne, and Henry the Lion, but recently back to his German estates, whose father-in-law, Henry of England, and son-in-law, Canute VI. of Denmark, promised their assistance. [Sidenote: