Bertharius (Italian: San Bertario di Montecassino) (c. 810 – 883) was a Benedictine abbot of Monte Cassino who is venerated as a saint and martyr. He was also a poet and a writer. A member of the Lombard nobility, Bertharius as a young man made a pilgrimage to Monte Cassino at the time of the abbacy of and decided as a result to become a monk. He became abbot in 856, succeeding Bassacius in that position. He became abbot at a critical time, in which Muslim incursions threatened central and southern Italy. The basilicas extra muros of Rome had been sacked in 846 AD.