Placidus was the son of Tertullus, a patrician, who dedicated Placidus as a boy to God and gave him to the care of St. Benedict. Placidus was miraculously rescued from drowning in a lake when in obedience to Benedict, the monk Maurus was able to run across the surface of the lake and rescue the boy. Little is known of Placidus’ later life. He was undoubtedly with St. Benedict when the monastery was moved to Monte Cassino. An ancient source says that Placidus was a martyr, but this is unlikely.