The death of the anti-Pope was a further blow to Frederick's cause, for the action of his representative in Italy committed him to recognise a second anti-Pope and laid him open to the accusation of desiring to perpetuate the schism. It seemed, however, as if his chance had come when the quarrel between Henry II and Thomas Becket drove the English Archbishop to take refuge with the Pope at Sens. Alexander was in a difficulty. Henry was perhaps the most powerful monarch in Europe, and his support was of the utmost importance to the Pope. But the rights for which Thomas was contending were part of the rights which Alexander himself was claiming against the Emperor--the right of the Church to manage her own concerns without lay interference. While, therefore, prudence forbade him to throw down a distinct challenge to the English King, it was impossible that he should comply with Henry's demand for the condemnation of the refractory Archbishop. Frederick took advantage of Henry's ill-humour to propose a marriage alliance between the royal houses and to sound Henry on the question of a change of alliance. The marriage thus arranged--of Frederick's cousin, Henry the Lion, to Henry II's daughter--ultimately took place. But both clergy and people in England were for the most part in sympathy with Becket and unwilling to prolong the schism. The altars used by Frederick's envoys in England were purified after their departure; and although Henry's representatives appeared at the Diet of Würzburg in May, 1165, and even took an oath to acknowledge the anti-Pope, the English King did not dare to ratify their action. [Sidenote: Frederick's momentary triumph.] Nor was this the only time when success seemed possible to Frederick. This failure to move the English allegiance and the defection of a number even of the German clergy emboldened Alexander to assume the aggressive, and he ventured to leave France and to take up his abode at Rome. (December, 1165.) Again the discontents of Lombardy were the occasion for the Emperor's visit. In the autumn of 1166 he crossed the Alps, and after spending some months in Lombardy he forced an entrance into Rome, enthroned his own Pope in St. Peter's, and himself wore his imperial crown. Frederick refused to treat with Alexander except on the basis of the resignation of both existing Popes and the election of a third. Alexander's position was unbearable and he fled to Benevento. The Romans accepted Frederick as their lord. The Emperor's triumph seemed complete: Charlemagne's successor had indeed arrived. But the triumph was short-lived. The summer pestilence, which so often attacked a German army in Italy, fell more fiercely than ever before. Frederick fled northwards before it, and found so much hostility in Lombardy that it was only by bypaths and in disguise that he was able to make his way out of Italy. [Sidenote: The Lombard League.]