Anastasius Bibliothecarius or Anastasius the Librarian (c. 810 – c. 878) was bibliothecarius (literally "librarian") and chief archivist of the Church of Rome and also briefly a claimant to the papacy. Early life He was a nephew of Bishop Arsenius of Orte, who executed important commissions as Papal legate. Anastasius learned the Greek language from Eastern Roman monks and obtained an unusual education for his era, such that he appears to be the most learned ecclesiastic of Rome in the 9th century. Abbot of Santa Maria and secretary of Nicholas I During the pontificate of Pope Nicholas I (858–867) Anastasius was abbot of Santa Maria in Trastevere on the farther side of the Tiber. He was employed by the pope in various matters. He was also active as an author, and translated Greek language works into Latin. Among them was the biography of St. John the Merciful, which he dedicated to Nicholas I. He has been shown by Ernst Perels to be the 'ghost-writer' behind much papal official correspondence of these years. The successor of Nicholas, Pope Adrian II (867–872), appointed Anastasius bibliothecarius (Head of archives) of the Roman Church, an important office at the Lateran Palace that gave him further influence at the Papal court. Envoy to Constantinople In 869 he was sent by Louis II, Holy Roman Emperor as envoy to Constantinople, with two men of high rank in the Frankish Empire, to negotiate a marriage between Leo VI the Wise, oldest son of the Eastern Roman emperor Basil I, and Louis's only child, Ermengard. When the envoys arrived at Constantinople, the Fourth Council of Constantinople was still in session, and Anastasius, who attended the last session (February, 870), zealously defended the papal cause and was of much service to the papal legates. On their way home the papal legates were robbed, and the "Acts" of the council were carried off. However, they had given most of the declarations of obedience of the Greek bishops to Anastasius, who also had a copy of the "Acts", and was thus able to bring these documents to the pope. At the pope's order, he translated the "Acts" into Latin. The Greek originals are lost. Continued influence The successor of Adrian II, Pope John VIII (872–882), also esteemed Anastasius, confirmed him in the office of librarian, entrusted important affairs to him, and encouraged him to further literary work. Anastasius was in correspondence