Helyot, Pierre a Franciscan monk of great learning (known also as father HIPPOLYTUS), was born at Paris in 1660, and died in 1716. He went twice to Rome on business of the order, and traveled through the whole of France. He is chiefly distinguished as the author of the Histoire des ordres monastiques religieux et militaires (Paris, 1714-21, 8 vols. 4to), of which he gathered the materials during his travels, and which is to this day the most complete work of the kind, though several of the orders are not treated in it. He died during the publication of the fifth volume, and the work was finished by Bullot. A new edition by Migne appeared at Paris in 1847-50 (4 vols. royal 8vo). See Lelong, Bibl. history de la France; Querard, La France litter.; Hoefer, Nouv. Biog. Géneralé. 23, 893.