Anastasius III Bibliothecarius (circa 810- 879) was an antipope of the Roman Catholic Church, during the year 855. He was known for his great learning, in an age where violence was abundant and scholars were in short supply. He was fluent in Latin and Greek, doing translations to Latin and also writing original works. Events October 1 - A man with a sword makes an attempt on emperor Nicephorus Is life. ... Events Wilfred the Hairy, Count of Barcelona, founded the benedictine monastery at Ripoll. ... Antipope Felix V, the last historical Antipope. ... The Roman Catholic Church, most often spoken of simply as the Catholic Church, is the largest Christian church, with over one billion members. ... The Roman Catholic Church is the largest Christian body in the world. ... Events Louis II succeeds Lothar as western emperor. ... Latin is the language originally spoken in the region around Rome called Latium. ...

He was chosen as pope when the ahderents of Louis II, Holy Roman Emperor managed to have the election of Pope Benedict III disavowed, only to later see Benedict be consecrated as pope anyway, under popular pressure. Pressure from the Emperor resulted in Anastasius being treated leniently, after his stint as an antipope. Louis II, (825 – 875), Holy Roman Emperor (sole ruler 855 – 875), eldest son of the emperor Lothair I, became the designated king of Italy in 839, and taking up his residence in that country was crowned king at Rome by Pope Sergius II on June 15, 844. ... Benedict III, prior to his election, had a reputation for learning and piety, and elected on the refusal of the initial choice of clergy and people, Hadrian: a group of important people preferred Anastasius. ...

Anastasius was called bibliothecarius because he later served as the librarian of the Church, being named such around 867 by Pope Adrian II at a time when this was an influential position in the papal court. He also held this position under Pope John VIII, Adrian's successor, probably till 879. The Librarian, a 1556 painting by Giuseppe Arcimboldo A librarian is a person who develops procedures for organizing information and provides services that assist and instruct people in the most efficient ways to identify and access any needed information or information resource (article, book, magazine, etc. ... Events September: Basil I becomes sole ruler of the Byzantine Empire. ... Adrian II (also known as Hadrian II),(792–872), pope from 867 to 872, was a member of a noble Roman family, and became pope in 867, at an advanced age. ... John VIII was pope from 872 to 882. ...

Anastasius undertook diplomatic work for the papal court, both in Italy and in foreign lands. He was ambassador for the Holy Roman Emperor Louis II to the Byzantine court of Basil I, the Eastern emperor, who had succeeded Emperor Michael III, the drunkard, by having him assassinated. This page is about negotiations; for the board game, see Diplomacy (game). ... The Byzantine Empire is the term conventionally used to describe the Roman Empire during the Middle Ages, centered at its capital in Constantinople. ... Basil, his son Constantine, and his second wife, emperess Eudoxia Ingerina. ... Michael III (839-867), the Drunkard, was grandson of Michael II, and succeeded his father Theophilus as Byzantine emperor when he was three years old in 842. ...

While in Rome, Anastasius met the orthodox monks Saint Cyril and Saint Methodius and supported their Christianizing efforts among the Slavs. This was before the great East-West Schism, which split the Catholic Church in two, so his support must not be taken as a brave and irresponsible act. See Saint Cyril (disambiguation) for other persons with this name. ... Saint Methodius was a Byzantine bishop of Great Moravia (Moravia) (born Thessaloniki, Byzantine Empire (today Greece), 826; he died in the (unknown) capital of Great Moravia, April 6, 885). ... The Slavic peoples are the most numerous ethnic and linguistic body of peoples in Europe. ... The East-West Schism, known also as the Great Schism (though this latter term sometimes refers to the later Western Schism), was the event that divided Chalcedonian Christianity into Western Catholicism and Eastern Orthodoxy. ...

According to some scholars, Anastasius the antipope and Anastasius the librarian are two different persons, while according to others they are one and the same.