After his death and burial at Civita Castellana in 1100 he was celebrated locally as a miracle-working saint, but Paschal II and the anti-imperial party soon subjected him to damnatio memoriae, which included the exhuming and dumping of his remains in the Tiber.

Owing to the active support of Duke Godfrey of Lorraine, of Archbishop Anno II of Cologne, and especially of Peter Damian, Alexander was soon recognized even in Germany and by Empress Agnes which may have been the reason of Guibert's dismissal in 1063 from the chancellorship.

[6] Guibert apparently continued to cultivate his contacts within the German court, for in 1072, Emperor Henry IV named him archbishop of the vacant see of Ravenna.

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.

[11][12][13] 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.

Gregory excommunicated Guibert by name at the Lenten Synod of February 1078 and with him his main accomplice Archbishop Tebaldo of Milan.

[16] With Rudolph of Swabia, leader of the rebellious nobles, having fallen mortally wounded at the Battle of Mersburg in 1080, Henry could concentrate all his forces against Gregory.

[20] By 1089, Clement III was back in Rome, where in June, he held a Synod declaring invalid the decree of excommunication launched against Henry, and various charges were made against the supporters of Urban II, the pope of the anti-imperial party.

[18] His followers elected a successor to Guibert, the Antipope Theodoric, who, however, was not a serious threat to the popes of the anti-imperial line, now considered canonical.