Adrian IV died and his successor, Pope Alexander III, soon proved to be in solidarity with the Italian municipalities and particularly hostile to the emperor. In 1163 the rebellion of some cities in northeastern Italy forced Frederick Barbarossa to descend for the third time in Italy in a military campaign that ended up in a stalemate, above all against the Veronese League, which in the meantime had formed between some cities of the March of Verona. With pacific Lombardy, Frederick in fact preferred to postpone the clash with the other municipalities of Northern Italy due to the numerical scarcity of his troops and then, after having verified the situation, he returned to Germany. The fourth military campaign in Italy and the Lombard League At the end of 1166 the emperor went to Italy for the fourth time at the head of a powerful army. To avoid the Marca of Verona, after having crossed the Alps from the Brenner Pass, instead of going along the usual Adige valley, Barbarossa turned towards Val Camonica; its objective was not, however, the attack on the rebellious Italian communes, but the Papacy. In fact, Frederick sided with the Antipope Paschal III, who in the meantime had ousted the legitimate pontiff, Alexander III, from Peter's throne; the latter, in 1165, after having obtained the recognition of the other European sovereigns, had returned to Rome, but Barbarossa, mindful of the role that his predecessors had on papal appointments, decided to intervene directly. As a test of strength, and for demonstration purposes, Frederick attacked some cities in Northern Italy, reaching Rome victorious, but an epidemic that spread among the ranks of the imperial army (perhaps of malaria) and which also affected the emperor himself, forced him to leave Rome, which in the meantime had surrendered, and to return precipitously to Northern Italy in search of reinforcements (August 1167). A few months before the epidemic that struck the imperial army, the municipalities of Northern Italy had joined forces in the Lombard League, a military union whose Latin name was Societas Lombardiae. According to the traditional narrative the municipalities sealed their alliance on 7 April 1167 with the oath of Pontida; this event, however, is questioned by historians for its lack of mention in contemporary chronicles and because the first mention of the oath is late, given that it appears in a document dated 1505. On 1 December 1167 the