St. Placidus, together with Maurus were committed to the care of St. Benedict, when both were very young. Their parents were friendly to the holy patriarch, who like them belonged to the nobility. St. Benedict had great love for these two early companions. On one occasion while drawing water from the lake of Subiaco, as St. Gregory relates, Placidus fell in and the waves carried him far from the shore. At the command of Benedict, Maurus hastened to the rescue and only after he had safely brought the young Placidus to the shore did he note that he had walked upon the waters. Little is known of the life of St. Placidus. Since the Tenth Century he has been venerated as a Saint in the Benedictine Order.
(Source: The New Roman Missal, Rev. F. X. Lasance)