Surname of LEO MARSICANUS, Benedictine chronicler, b. about 1045; d. 22 May, 1115, 1116, or 1117. He belonged to an old noble family, and at the age of fourteen entered Monte Cassino, where his talents soon won him the regard of Abbot Desiderius, later Pope Victor III. Desiderius entrusted his education to the future Cardinal Aldemar. On the completion of his studies, Ostiensis became librarian and archivist of the monastery, and, as such, his main task was to settle, in accordance with the existing documents, all disputes concerning landed property in which the monastery became involved. Abbot Oderisius, who succeeded Desiderius, urged Ostiensis to write a history of the monastery, but, on account of his numerous duties, he was unable to give himself entirely to the work. Paschal II created him Cardinal Bishop of Ostia. In the conflict between the pope and Henry V, Ostiensis vigorously defended the papacy. His unfinished chronicle, originally called "Legenda sancti Benedicti longa", treats the period between 529 and 1075; Petrus Diaconus continued it to 1139. Trustworthy and impartial, the chronicle is a valuable mine of information for the history of Lower Italy, but as the documents on which the narrative rests are still extant, it has no special importance for our knowledge of the time. It was first edited under the title, "Chronica sacri monasterii Casinensis auctore Leone cardinal episcopo Ostiensi", by Abbot Angelus de Nuce (Paris, 1668); then by Wattenbach in "Monumenta Germaniae: Scriptores", VII, 574-727, and Migne in "P.L.", CLXXIII, 479-763. Ostiensis has left several lesser works: "Narratio de consecratione ecclesiarum a Desiderio et Oderisio in Monte Casino aedificatarum" (P.L., CLXXIII, 997-1002), and "Vita sancti Mennatis eremitae et confessoris" (edited in part, P.L., CLXXIII, 989-92).
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