See J. Langen, _Geschichte der romischen Kirche von Gregor VII. bis Innocenz III._ (Bonn, 1893); Jaffe-Wattenbach, _Regesta pontif. Roman_. (2nd ed., 1885-1888); 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, 1900-1902); and O. Kohncke, _Wibert von Ravenna_ (Leipzig, 1888). (C. H. Ha.) GUIBERT (1053-1124), of Nogent, historian and theologian, was born of noble parents at Clermont-en-Beauvoisis, and dedicated from infancy to the church. He received his early education at the Benedictine abbey of Flavigny (Flaviacum) or St Germer, where he studied with great zeal, devoting himself at first to the secular poets, an experience which left its imprint on his works; later changing to theology, through the influence of Anselm of Bec, afterwards of Canterbury. In 1104, he was chosen to be head of the abbey of Notre Dame de Nogent and henceforth took a prominent part in ecclesiastical affairs. His autobiography (_De vita sua, sive monodiarum_), written towards the close of his life, gives many picturesque glimpses of his time and the customs of his country. The description of the commune of Laon is an historical document of the first order. The same local colour lends charm to his history of the first crusade (_Gesta Dei per Francos_) written about 1110. But the history is largely a paraphrase, in ornate style, of the _Gesta Francorum_ of an anonymous Norman author (see CRUSADES); and when he comes to the end of his authority, he allows his book to degenerate into an undigested heap of notes and anecdotes. At the same time his high birth and his position in the church give his work an occasional value.