ANASTASIUS THE LIBRARIAN. - Born probably in Rome around 817, he received a solid Latin and Greek cultural formation in the urban monasteries. Created cardinal priest of S. Marcello by Leo IV around 847, he was excommunicated and struck with anathema in a synod held in Rome on 19 June 853 for having abandoned his post and refused to return despite repeated summons. Ambitious, of very high self-esteem, he was active in the imperial party in the hope of ascending to the papal throne. In 855, immediately after the election of Benedict III, he returned to Rome with a strong army, but his attempt to occupy the Lateran failed. Defeated, he received the Pope’s pardon and was reduced to the lay state. When Nicholas I ascended the papal throne in 858, Anastasius returned to favor and became the Pope’s advisor, a position he maintained under the subsequent pontificates of Adrian II and John VIII, becoming one of the most important figures of the time. He played a significant role in the controversies with Photius, which opened the schism of the Eastern Church. He attended the final session of the Eighth Ecumenical Council in Constantinople (869–70), from which he brought back to Rome a copy of the Acts, which, at the invitation of Adrian II, he translated into Latin (871), and which is the only one preserved. Later (873), by order of John VIII, he also translated into Latin the Acts of the Seventh Ecumenical Council, held at Nicaea (787).
After 877 Anastasius’ name no longer appears in the documents, and the year of his death is unknown.
Almost all of Anastasius’ works are Latin translations from Greek. Among these, those concerning ecclesiastical history are particularly noteworthy: *Versiones gestorum synodorum VII et VIII* (PL 129, 205–542, 27–196); *Collectanea*, i.e., translations concerning the question of Monothelitism and Pope Honorius I (ibid., 557–690); *Acta s. Martini papae* (ibid., 585–609); *Historia ecclesiastica* (ed. C. De Boor, *Theophanis Chronographia*, II, Leipzig 1885, pp. 31–346), expanded in accordance with the *Tripartite History* of Cassiodorus from the histories of Nicephorus, Syncellus, and Theophanes, translated into Latin by Anastasius. The remainder of his works are translations of the lives of Greek saints. To each of these Anastasius prefixed prefaces or explanatory letters (MGH, *Epist.*, VII, pp. 395–442), some of which are of singular importance, especially those relating to the Acts of the Seventh and Eighth Councils (ibid., pp. 403–418).
Anastasius was erroneously attributed by Onofrio Panvinio with the *Liber Pontificalis*, an attribution often repeated down to the present day. It seems, however, beyond doubt that he is the author of the life of Nicholas I, though there are scholars who contest this.