Placide de Sainte Hélène (1648 - 1734), aka Placidium Augustinum, was a French geographer and Augustine monk. He is the brother of the French royal geographer to King Louis XIV, Pierre Du Val (1619 - 1683). He took orders in Augustine orders in 1666. In 1705, he was awarded the position of Géographe Ordinaire du Roi. Placidus, as he is known, contributed significantly to French and Dutch cartography in the late 17th and early 18th centuries. His name appears on dozens of maps, some very significant. He also completed a study of the Course of the Po River.