The relationship between Pope Leo I (440–61) and Prosper of Aquitaine has been problematic for centuries. Following on from Gennadius’ late fifth-century rumour about Prosper’s involvement with Leo’s letters against Eutyches, Prosper has been cast as Leo’s secretary, adviser or ghostwriter for all or some of Leo’s works. 1 Scholars have assumed that Leo, as bishop of Rome, was either too busy or too theologically unsophisticated to be able to craft his own letters, sermons and treatises. Yet, even among scholars who see Prosper as Leo’s theological ghostwriter, there is no agreement on when the two men met, if they did. Some scholars propose an initial meeting in 431 when Leo was archdeacon and Prosper went with Hilary from Marseille to Rome to inform Celestine I, then bishop of Rome, about Pelagianism in Gaul. 2 Others suggest the two men met in 440, when Leo was in Gaul on a diplomatic mission before his episcopal election. 3 In any case, it is widely stated that Prosper was in Rome either by 435 or, at the latest, by 440 so that he could serve Leo, now pope. 4 Their presumed relationship lies behind scholarly assessment of many of their works; so, for example, Muhlberger presumes their bond to explain in part why Prosper’s Chronicon makes Leo into the paradigm of a saint and the key figure in his account of events. 5