Anastasius Bibliothecarius
| Antipope Anastasius III | |
|---|---|
| Papacy began | c. 17 July 855 | 
| Papacy ended | c. 29 September 855 | 
| Predecessor | Roman claimant: Leo IV Antipapal claimant: John VIII | 
| Successor | Roman claimant: Benedict III Antipapal claimant: Christopher | 
| Other post(s) | Abbot of Santa Maria in Trastevere Bibliothecarius of the Roman Catholic Church | 
| Personal details | |
| Born | c. 810 | 
| Died | c. 878 | 
Anastasius Bibliothecarius (c. 810 – c. 878) was the chief archivist and librarian (bibliothecarius) of the Holy See and also briefly a claimant to the papacy.