Bertharius was a 9th-century Benedictine abbot of Monte Cassino who belonged to the Lombard nobility. After visiting the abbey as a young man, he chose to enter the monastic life. He rose to lead the monastery in 856, a period marked by significant threats from Muslim incursions in southern Italy. During his leadership, he worked to protect the abbey and expanded its influence by founding a new monastery for women at Teano.