Saint Placid (also known as Saint Placidus) was the oldest son of the patrician Tertullus. Roughly around the age of 8, he was brought to Subiaco and placed under the care of Saint Benedict. He died sometime in the 6th century but very little is known of his life. His name was found in the Litany of Saints in an ancient psalterium at Vallombrosa and in Codex CLV at Subiaco.
One surviving story written by Saint Gregory the Great in his Dialogues II recounts that Saint Placidus was drowning in a lake. Saint Benedict ordered Saint Maurus to save him and miraculously, Saint Maurus ran across the surface of the lake, rescued Saint Placidus and brought him safely back to shore.