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A converted Jew and controversialist, born at Huesca, in the former Kingdom of Aragon, 1062; died 1110. Previous to his conversion he was known as Moses Sephardi (the Spaniard). King Alfonso I of Aragon, whose physician-in-ordinary he became, stood sponsor at his baptism, which he received in his native town on St. Peter's day (29 June, 1106). In honour of this saint and of his sponsor he chose the name Petrus Alfonsus. As his conversion was attributed by his former co-religionists to ignorance or dishonourable motives, he published a justification in a Latin work consisting of twelve dialogues between a Jew and a Christian. These dialogues were first printed at Cologne in 1536, and have since frequently been re-edited. A second work of Petrus Alfonsus, based on Arabic sources, is entitled "Ecclesiastical Discipline" (Disciplina Clericalis). It has been translated into several languages and is preserved in numerous manuscripts. Labouderie, Vicar-General of Avignon, published it at Paris in 1824 with a French translation of the fifteenth century. Another edition by F. W. V. Schmidt appeared at Berlin in 1827. The text of both works of Petrus Alfonsus, preceded by biographical notices, may be found in Migne, CLVII, 527-706.

CEILLIER, Auteurs ecclésiast., XIV (Paris, 1863), i, 170-73; KOHUT in Jewish Encycl., I, 377; DOUCE in BOHN'S Antiq. Libr., X (London, 1848), 39-44.

N. A. WEBER.