ADSO: One of the more prominent of the reforming abbots of the tenth century. He belonged to a noble family in the Jura Mountains, became a monk at Luxeuil, and went later to the monastery of Montier-en-Der (120 m. e.s.e. of Paris), in the diocese of Châlons-sur-Marne, reformed about 935 by the abbot Albert, whom he succeeded in 967 or 968. He laid the foundation for a splendid new basilica, remains of which are still standing (cf. Sackur, Die Cluniacenser, ii. 391), and undertook to reform other monasteries, e.g., St. Benignus at Dijon. Like his friends Abbo of Fleury and Gerbert of Reims (cf. Havet, Les Lettres de Gerbert, pp.6, 74, Paris, 1889), he was interested in learning and investigation; and his library included the writings of Aristotle, Porphyry, Terence, Caesar, and Vergil. He was often urged to write books, especially the lives of saints, and several works of this class by him may be found in ASM (ii. and iv.; copied in MPL, cxxxvii. 597-700).

The most famous of Adso's writings is the earliest, an Epistola ad Gerbergam reginam, de vita et tempore Antichristi, composed before 954, in which he opposes the prevalent notion that the appearance of Antichrist was near at hand. The work was much read, and suffered greatly from mutilations and interpolations (cf. MPL, ci. l289-98); its original form has been restored by E. Sackur, in Sibyllinische Texte und Forschungen, pp.104-113, Halle, 1898.

BIBLIOGRAPHY: The chief source for Adso's life is an addition of the eleventh century to his Vita S. Bercharii, the patron saint of Montier-en-Der, ch xi., in MPL, cxxxvii. 678-679, and in MGH, Script., iv. (1841) 488. Consult also the Histoire litteraire de la France, vi. 471-492; A. Ebert, Allgemeine Geschichte der Litteratur des Mittelalters im Abendlande, iii. 472-484, Leipsic, 1887; and, especially, E. Sackur, Die Cluniacenser, vol. i., Halle, 1892.