GUIBERT or WIBERT (c. 1030-1100), of Ravenna, anti pope under the title of Clement III. from June 25, io8o until September i Ioo, was born at Parma between and of the noble imperialist family, Corregio. He was appointed by the empress Agnes, chancellor and, after the death of Pope Victor II. (1057), imperial vicar of Italy. He strove to uphold the imperial authority during Henry IV.'s minority, and presided over the synod at Basel (1o61). Guibert lost the chancellorship in 1062. In 1073, through the influence of Empress Agnes and the support of Cardinal Hildebrand, he obtained the archbishopric of Ravenna and swore fealty to Alexander II. and his successors. He seems to have been at first on friendly terms with Gregory VII., but soon quarrelled with him over the possession of the city of Imola, and henceforth was recognized as the soul of the imperial faction in the investiture contest. He allied himself with Cencius, Cardi nal Candidus and other opponents of Gregory at Rome, and, on his refusal to furnish troops or to attend the Lenten synod of 1075, he was ecclesiastically suspended by the pope. He was probably excommunicated at the synod of Worms (1076) with other Lombard bishops who sided with Henry IV., and at the Lenten synod of 1078 he was banned by name. The emperor, having been excommunicated for the second time in March o8o, convened 19 bishops of his party at Mainz on May 31, who pro nounced the deposition of Gregory; and on June 25 he caused Guibert to be elected pope by 3o bishops assembled at Brixen. Guibert was installed in the Lateran and consecrated as Clement III. on March 24, 1084. One week later, on Easter Sunday, he crowned Henry IV. and Bertha in St. Peter's. Clement survived not only Gregory VII. but also Victor III. and Urban II., main taining his title to the end and in great measure his power over Rome and the adjoining regions. Excommunication was pro nounced against him by all his rivals. He was driven out of Rome finally by crusaders in 1097, and sought refuge various for tresses on his own estates. St. Angelo, the last Guibertist strong hold in Rome, fell to Urban II. on Aug. 24, 1098. Clement, on the accession of Paschal II. in 1o99, prepared to renew his struggle but was driven from Albano by Norman troops and died at Civita Castellana in September iroo.
See J. Langen, Geschichte der romischen Kirche von Gregor VII. bis Innocenz III. (Bonn, 1893) ; Jaffe-Wattenbach, Regesta pontif. Roman (2nd ed., 1885-88) ; K. J. von Hefele, Conciliengeschichte, vol. v. (2nd ed.) ; F. Gregorovius, Rome in the Middle Ages, vol. iv., trans. by Mrs. G. W. Hamilton (London, 19oo—o2) ; and O. Kohncke, Wibert von Ravenna (Leipzig, '888). (C. H. H.)