A cleric, he was appointed to the Imperial Chancellorship for Italy by the Empress Agnes in 1057, which position he held until 1063. In 1058 he participated in the election of Pope Nicholas II but on his death in 1061, he combined with the Imperial and Transpadine Anti-Reform party to create Cadalous of Parma as Antipope Honorius II against Pope Alexander II. However, owing to the campaigns of Duke Godfrey of Lorraine, Archbishop Anno of Cologne, and St. Peter Damian, the Church by-and-large rejected Honorius II and acknowledged Alexander II; probably as a result of these activities, the Empress Agnes dismissed him from the Imperial Chancellorship of Italy.
Guibert laid low for the next nine years, but 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. And, although Pope Alexander II was reluctant to confirm this appointment, he was prevailed by Hildebrand to do so, perhaps as a compromise for peace. Guibert then took an oath of allegiance to the Holy Father and his successors and was installed at Ravenna in 1073.
Shortly after Pope Alexander II died and Hildebrand was elected the next pope, being installed as Pope Gregory VII on April 29, 1073. Guibert attended the first Lenten Synods of Pope Gregory in March 1074 in Rome, and at which important laws were passed against simony and the incontinence of the clergy, but 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 it. By his absence he made manifest his opposition to Gregory VII, who now suspended him for his refusal to attend the synod.
The main cause of the quarrel was Pope Gregory's insistence of ending clerical concubinage and simony and of ejecting from the ministry refractory bishops and priests who continued to keep their concubines.
It was in this same year that Emperor Henry IV began his open war on Gregory. At a synod held at Worms in January, 1076, a resolution was adopted deposing Gregory, and in this decision the simoniacal bishops of Transpadine Italy joined. Among these must have been Guibert, for he shared in the sentence of excommunication and interdiction which Gregory VII pronounced against the guilty Transpadine bishops at the Lenten Synod of 1076.
Shortly after, in April 1076, bishops and abbots of the Transpadine anti-reform party convened at Pavia under the presidency of Guibert and proclaimed the excommunication of Gregory VII; a messenger, bearing a most offensive personal letter from Henry, was dispatched with the Pavian reply to the pope. In response, Gregory was compelled to resort to still stronger measures with regard to Guibert; he excommunicated Guibert by name at the Lenten Synod of February, 1078, and with him his main accomplice Archbishop Tebaldo of Milan.
On account of the action of Henry's 1076 Synod of Worms against Gregory, the latter was compelled to lay Henry IV under excommunication.
Gregory's measures against Henry provided an opportunity to the nobles of Germany who were discontented with him and they began steps to depose him, thus rendering Henry's position precarious.
At first he was encouraged by his party to resist, but his friends, including his abettors among the episcopate, began to abandon him, and the Saxons revolted once more, demanding a new monarch.
At a Congress held at Tibur by the German spiritual and temporal lords, in October, 1076, the election of a new emperor was canvassed. On learning through the papal legate of Gregory's desire that the crown should be reserved for Henry if possible, the assembly contented itself with calling upon him to abstain for the time being from exercising administrative offices and to avoid the company of those who had been excommunicated, but declared his crown forfeited if he were not reconciled with the pope within a year.
It was further agreed to invite Gregory to a council at Augsburg in the following February, at which Henry was summoned to present himself.
As the majority of the princes of the empire now took sides against the king, Henry urgently sought to be reconciled with the pope, and consequently travelled to Italy in the middle of a severe winter, in order to meet the pope there before the latter should leave Italian soil on his journey to Germany.
Abandoned by his own partisans and fearing for his throne, Henry fled secretly with his wife and child and a single servant to Gregory to tender his submission. He crossed the Alps in the depth of one of the severest winters on record. On reaching Italy, anti-reform Italians flocked around him promising aid and assistance in his quarrel with the pope, but Henry spurned their offers.
Gregory, who was already on his way to Augsburg, had already arrived in Lombardy when he heard of the king's journey; fearing treachery, Gregory retreated to the mountain stronghold of Canossa for security. Henry followed him there, but the Pope, mindful of his former faithlessness, treated him with extreme severity.
The excommunicated king requested Countess Matilda, his mother- in-law Adelaide, and Abbot Hugh of Cluny, to intercede with the pope for him. On their intercession, and after long opposition, Gregory permitted Henry to appear before him personally at Canossa and atone for his guilt by public penance.
Stript of his royal robes, and clad as a penitent, Henry had to come barefooted through ice and snow, and crave for admission to the presence of the pope. All day he remained at the door of the citadel, fasting and exposed to the inclemency of the wintry weather, but was refused admission. A second and a third day he thus humiliated and disciplined himself, and finally on January 28, 1077, he was received by Pope Gregory and absolved from censure, but only on condition that he would appear at the proposed council and submit himself to its decision.
After the king's departure the pope set out for Mantua. For safety Countess Matilda accompanied him with armed men, but hearing a rumour that Archbishop Guibert of Ravenna, who was unfriendly to Gregory, was preparing an ambush for him, she brought the pope back to Canossa.
Henry then returned to Germany, but his severe lesson failed to effect any radical improvement in his conduct. Disgusted by his inconsistencies and dishonesty, the German princes on March 15, 1077, elected Rudolph of Swabia to succeed him. Gregory wished to remain neutral, and even strove to effect a compromise between the opposing parties. Both, however, were dissatisfied, and prevented the proposed council from being held. Henry's conduct toward the pope was meanwhile characterized by the greatest duplicity, and, when he went so far as to threaten to set up an antipope, Gregory renewed his decree of anathema and excommunication against Henry in March, 1080.
Carrying out his threats, Henry summoned his German and Transpadine partisans to a Synod at Brixen in June, 1080, which drew up a new decree purporting to depose Pope Gregory VII, and which Henry himself also signed, and then proceeded to elect Guibert, the excommunicated simoniacal Archbishop of Ravenna, as antipope in opposition to Pope Gregory; Guibert took the name Clement III. Henry at once recognized Guibert as pope, swearing that he would lead him to Rome, and there receive from his hands the imperial crown.
The antipope failed to secure recognition outside of Henry's dominions and was widely understood as being merely his puppet and quite devoid of personal initiative.
Rudolph of Swabia having fallen mortally wounded at the Battle of Mersburg in 1080. Henry could concentrate all his forces against Gregory. In 1081 he marched on Rome, but failed to force his way into the city, which he finally accomplished only in 1084.
Gregory thereupon retired into the citadel of Sant' Angelo, and refused to entertain Henry's overtures, although the latter promised to hand over Guibert as a prisoner, if the Pope would only consent to crown him emperor.
Gregory, however, insisted as a necessary preliminary that Henry should appear before a council and do penance. The emperor, while pretending to submit to these terms, tried hard to prevent the meeting of the bishops. A small number however assembled, and, in accordance with their wishes, Gregory again excommunicated Henry.
The latter on receipt of this news again entered Rome on March 21, 1084, and succeeded in gaining possession of the greater part of the city and besieged the Pope in the Castle of Sant' Angelo, while, on March 24, Guibert was enthroned as pope in the church of St. John Lateran as Clement III, and on March 31 Guibert crowned Henry IV emperor at St. Peter's.
However, when the news was brought that Gregory's Norman ally Robert Guiscard Duke of Normandy was hastening to his aid, Henry fled Rome with Guibert and, in revenge for Matilda's staunch support for Gregory and the reform party, ravaged her possessions in Tuscany.
The Pope was liberated, but, the people becoming incensed by the excesses of his Norman allies, he was compelled to leave Rome. Disappointed and sorrowing he withdrew to Monte Cassino, and later to the castle of Salerno by the sea, in 1084, where he died in the following year, May 25, 1085.
Three days before his death he withdrew all the censures of excommunication that he had pronounced, except those against the two chief offenders Henry and Guibert. His last words were:
- "I have loved justice and hated iniquity, therefore I die in exile."
The German episcopate stood divided. While anti-simonical bishops held a Synod in Quedlinburg, at which they denounced and condemned Guibert, partisans of Henry held a rival Synod at Mainz in 1085, where they approved the deposition of Gregory and the elevation of Guibert.
This conflict continued even after the death of Gregory, during the entire reigns of whose successors, Pope Victor III, Pope Urban II, and Pope Paschal II, Guibert figured as the antipope of Henry and his party.
Victor III, who was elected after a prolonged vacancy caused by the critical position of the Church in Rome, was compelled, eight days after his coronation in St. Peter's on May 3, 1087, to fly from Rome before the partisans of Guibert. The latter were in turn assailed by the troops of Countess Matilda, and entrenched themselves in the Pantheon.
The succeeding pope, Urban II (1088-1099), was at one time master of Rome, but he was afterwards driven from the city by the adherents of Guibert, and sought refuge in Lower Italy and in France.
In June, 1089, at a Synod held in Rome, the antipope declared invalid the decree of excommunication launched against Henry, and various charges were made against the supporters of the legitimate pope.
Still, the years which followed brought to Urban ever-increasing prestige, while Henry IV's power and influence were more and more on the wane.
The greater part of the city of Rome was captured by an army of crusaders under Count Hugh of Vermandois, brother of the King of France. The party of Guibert retained only the Castle of Sant' Angelo, and even this in 1098 fell into the hands of Vermandois.
Guibert's influence, after Henry IV's withdrawal from Italy, was virtually confined to Ravenna and a few other districts of Northern Italy.
In 1099, he repaired to Albano after the accession of Paschal II (1099-1118), hoping again to become master of Rome, but he was compelled to withdraw. He reached Cività Castellana, where he died September 8, 1100. His followers, it is true, elected a successor to Guibert, the Antipope Theodoric, who, however, was not a serious threat to the true popes.
The elevation of Guibert has to be seen in the wider context of the time: there had been several antipopes in the recent past, there were political struggles within the empire, and the Investiture Crisis also had an effect.
Clement was notoriously regarded as the champion of the simoniacal and anti-celibacy and pro-clerical concubinage party, although he went through the notions of legislating against these abuses, and, through the leeway he granted the cardinals supporting him, contributed to the development of the College of Cardinals.