PROSPER OF AQUITAINE or PROSPER TIRO (c. 390- c. 465), Christian writer and disciple of St. Augustine, was a na tive of Aquitaine, and seems to have been educated at Marseilles. In 431 he appeared in Rome to interview Pope Celestine re garding the teachings of St. Augustine and then all traces of him are lost until 44o, the first year of the pontificate of Leo I., who had been in Gaul and thus probably had met Prosper. In any case Prosper was soon in Rome, attached to the pope in some secretarial or notarial capacity. Gennadius (De script. eccl. 85) mentions a rumour that Prosper dictated the famous letters of Leo I. against Eutyches. The date of his death is not known, but his chronicle goes as far as 455, and the fact that Ammianus Marcellinus mentions him under the year 463 seems to indicate that his death was shortly after that date. Prosper attacked the Pelagians in a polemical poem of about i,000 lines, Adversus ingratos, written about 43o. After Augustine's death he wrote three series of Augustinian defences, especially against Vincent of Lerins (Pro Augustine responsiones). His chief work was against Cassian's Collatio, his De gratin dei ut libero arbitrio (432). He also induced Pope Celestine to publish an Epistola ad
episcopos Gallorum against Cassian. He corresponded with Augus tine and made an abridgment of his commentary on the Psalms, a collection of sentences from his works. He also put into elegiac metre, in io6 epigrams, some of Augustine's theological dicta.
Prosper's Epitoma chronicon is a careless compilation from St. Jerome in the earlier part, and from other writers in the later, but the lack of other sources makes it very valuable for the period from 425 to 455 of which he had personal knowledge. There were five different editions, the last of them dating from 455, after the death of Valentinian. For a long time the Chronicon imperials was also attributed to Prosper Tiro, but without the slightest justification, for it exhibits Pelagian tendencies.
The Chronicon has been edited by T. Mommsen in the Chronica minora of the ,/lfonumenta Germaniae historica (1892). The com plete works are in Migne's Patrologia latina. Tome 51. See L. Valen tine, St. Prosper d'Aquitaine (Paris, 19oo) and A. Potthast Bibliotheca historica; (5896).