Hildebrand to do so, perhaps as a compromise for peace. Guibert then took an oath of allegiance to the pope and his successors and was installed at Ravenna in 1073. Quarrels with Pope Gregory Shortly after Pope Alexander II died Hildebrand was proclaimed the next pope, being installed as Pope Gregory VII on 29 April 1073. Guibert attended the first Lenten Synods of Pope Gregory in March 1074 in Rome at which important laws were passed against simony and the incontinence of the clergy, and lay investiture. The Imperial appointed German bishops were the most important officials of the empire, and a means to balance the ambitions of the territorial princes. Guibert soon emerged as one of the most visible leaders of opposition to the Gregorian reforms. Having attended Gregory's first Lenten Synods, Guibert refused to attend the next, the Lenten Synod of 1075, although he was bound by oath to obey the summons to attend. Guibert was unsympathetic to Gregory's opposition to the Imperial Court, which Guibert had served as Chancellor of Italy. By his absence Guibert demonstrated his opposition to Gregory VII, who now suspended him for his refusal to attend the synod. It was in this same year that Emperor Henry IV began his open conflict with Gregory. At the synod of Worms in January 1076, a resolution was adopted deposing Gregory, and in this decision the pro-imperial bishops of Transalpine Italy joined. Among these must have been Guibert, for he shared in the sentence of excommunication and interdiction which Gregory VII pronounced against the Transalpine bishops at the Lenten Synod of 1076. Shortly after, in April 1076, bishops and abbots of the imperial Transalpine party convened at Pavia under the presidency of Guibert and proclaimed the excommunication of Gregory VII; a messenger, bearing a caustic personal letter from Henry, was dispatched with the Pavian reply to the pope. In response to the action of Henry's 1076 Synod of Worms, Gregory excommunicated Henry IV. Gregory excommunicated Guibert by name at the Lenten Synod of February 1078 and with him his main accomplice Archbishop Tebaldo of Milan. Reign as Imperial Opposition Pope During the next four years, the Emperor and the Pope reconciled but then quarreled again, and, facing a rebellion among the German nobles, Emperor Henry threatened to depose Pope Gregory. Carrying out his threats, Henry summoned his German and Transpadine partisans to a Synod at Brixen