Argaiz, Gregorio was a Spanish Benedictine of the 17th century. In a monastery of Old Castile he wrote a history of the Spanish Church, entitled Poblacion Eclesiastica de Espana, y Noticia de sus Primeras; Honras Hallada en los Escritos de San Gregorio, Obispo de Granzada, y en la Cranica de Hauberto, Monge de San Benito. The first volume of this work was published at Madrid in 1667, the second in 1668, and two others in 1669. Argaiz was convicted of having forged the documents from which he had written this work; but this was one of the frauds considered justifiable by the ecclesiastics. He. published in .1675 a defence of his work entitled instruccion Historica apologetica para Religiosos, Eclesiasticos, y Seglares (Madrid). Besides several other works, he also wrote Teatro Monastico y Obispos de Espania, which was never published. See Hoefer, Nouv. Biog. General, s.v.