Prosper of Aquitaine

Prosper of Aquitaine (c. 390–c. 463) was a Latin theologian, lay monk, and the most ardent defender of Augustinian theology in the generation after Augustine's death. Writing from Marseille amid the Semi-Pelagian controversies, he championed Augustine's teaching on grace and predestination against John Cassian and the monks of southern Gaul, and later settled in Rome as a close aide — likely secretary — to Pope Leo I, by c. 435–440. He coined the influential liturgical axiom *ut legem credendi lex statuat supplicandi* ("let the law of prayer establish the law of belief"), which in later transmission was reversed and recast as the abbreviated *lex orandi, lex credendi* (with *supplicandi* replaced by *orandi*). As the first continuator of Jerome's universal chronicle and the probable author of *De vocatione omnium gentium*, he became a vital conduit of Augustinian thought to the medieval West.