Shortly after his accession Frederick had made an agreement with the then Pope that neither should make peace with the Romans or the Sicilian King without consent of the other. But now Hadrian, deserted, accepted the Commune as the civil authority in Rome, and even came to a treaty with William of Sicily, who engaged to hold all his lands as a vassal of the Pope. Frederick was naturally angry at the repudiation of the mutual obligation with regard to peace and of the imperial suzerainty of William's duchy of Apulia. But he was too much occupied in Germany to do more than protest. And before he was able to assert his power in Italy again Pope Hadrian had, as it were, thrown down a challenge to him. At the Diet of Besançon in Burgundy in 1157 two papal envoys appeared with a complaint of Frederick's conduct in some particular. The letter which they bore spoke of the late coronation of the Emperor by the Pope and used the equivocal word _beneficia_ to describe the papal act. When the assembled nobles resented the expression as implying a feudal relation between Pope and Emperor, the papal representative, the Chancellor Roland, boldly asked, "From whom, then, does the emperor hold the empire if not from the Pope?" Frederick's authority alone saved the envoys from violence, and Hadrian found himself obliged to explain away the objectionable expressions. [Sidenote: The breach.] But the papal position had been formulated, and that before a German assembly. The Pope was no longer a suppliant: he claimed to be more than an equal. He had thrown down a challenge. Frederick proceeded to pick it up. In fact, it was this second expedition of Frederick to Italy which opened the long contest between Ghibelline and Guelf, a contest only to be ended by the practical destruction of one or other of the parties. It was the complaints of the other cities against the oppression of Milan, which were the immediate cause of Frederick's appearance in Italy in 1158; and the reduction of the Milanese was followed by the holding of an assembly on the plain of Roncaglia, to which Frederick summoned the most famous lawyers of Italy. By their decision rights and powers were given to him, which placed all the communes at his mercy. Moreover, these were not compatible with the rights asserted since the time of Gregory VII by the papal supporters: the regalia were given to the Emperor at the expense of ecclesiastical as well as lay landowners and corporations. If the papal investiture of Apulia infringed the imperial rights, the investiture of Frederick's uncle, Welf VI of Bavaria, with the inheritance of the Countess Matilda openly ignored the oft-repeated claim of the Papacy. Neither side seemed to take especial pains to avoid a breach. The acrimonious correspondence which ensued centred round the relations of the Italian bishops to the Emperor, the respective claims of each party to Rome, and the restoration of the Tuscan inheritance and all