c.810-c.880. Antipope. Family connections and a knowledge of Greek learned from Greek monks resident in Italy helped his early promotion to cardinal- priest by about 847. Unexplained events led to his excommunication (850), anathematization, and deposition (853). In 855 Benedict III was elected pope, but a rival group chose Anastasius, who captured the Lateran Palace and Benedict himself. The imperial legate mediated in favor of Benedict, who forgave Anastasius, and henceforward the latter remained a loyal and influential official. Abbot of Santa Maria, Trastevere (858-67), he then became papal librarian (hence “Bibliothecarius”). In 868 a cousin murdered Pope Adrian II's daughter and her mother; this was a temporary setback to Anastasius's fortunes, but by 869 he was back in papal favor and acting unsuccessfully as Louis II's negotiator in Constantinople for a marriage between his daughter Ermengard and the Eastern emperor Basil I's son. In Constantinople Anastasius successfully championed the papal claims of supremacy at the Eighth Ecumenical Council ( , 869-70) which upheld 's deposition of the Byzantine Patriarch Photius* and condemned his heretical teachings. Later Anastasius translated into Latin the Acts of this council and of the Seventh Council at Nicea (787). He also wrote a number of saints' lives, the Chronographia Tripartita (derived from Byzantine chronicles), and translated many Greek religious works.