The ‘Chronicon’ makes a second reference to Palladius, stating that two years later (431) he was sent by Celestine ‘as the first bishop to the Irish believing in Christ’. Prosper's statement has a number of important implications, one being that there was already a community of Christians in Ireland of which Celestine was aware. There is also the probability that the Irish had made representation to Rome to have a bishop appointed. Prosper makes a further significant, albeit indirect, reference to Palladius. In his treatise ‘Contra collatorem’ (433), directed against Cassian of Marseilles, he writes that Celestine, ‘having ordained a bishop for the Irish, while he labours to keep the Roman island [Britain] Catholic, he has also made the barbarian island [Ireland] Christian’. Prosper, who was certainly in a position to know the situation, regarded the initiatives in relation to countering Pelagianism in Britain and ministering to Christians in Ireland as elements of the same papal programme. He was writing in the present tense, apparently in the belief that, contrary to later Irish tradition, Palladius's mission was successful and still in progress. There is, however, no direct evidence as to the duration of the mission.
Although he was based in Rome for a time, there is no evidence that Palladius was Roman in origin; the circumstantial evidence suggests that he was originally Gaulish and perhaps a cleric of the church of Auxerre. The name is well attested for fourth- and fifth-century Gaul. It is possible that Palladius is the person of that name mentioned in the poem, ‘De reditu suo’, written c.418 by the Gaulish nobleman Rutilius. The great liturgiologist Gamber has plausibly conjectured that Palladius brought Roman mass texts with him to Ireland and that they formed part of the basis of early Irish liturgy. It is also possible that Palladius was the originator of the so-called ‘Dicta Patricii’.
The evidence suggests that by the seventh century the history of the missions of Patrick and Palladius had become confused. It appears that later (seventh- and eighth-century) propaganda emanating from the church of Armagh appropriated Palladius's mission to Patrick. It created the fiction that either Palladius's mission had failed or that he had died soon after arrival. In either case it was claimed that it began and ended in 431. The beginning of Patrick's mission was accordingly set at 432. It is probable that the three bishops with distinctively Gaulish names – Secundinus (qv) (d. c.447), Auxilius (qv) (d. 459), and Iserninus (qv) (d. 468) – sent, according to the Annals of Ulster, in 439 in auxilium Patricii, ‘as an aid to Patrick’, were actually reinforcements for Palladius's mission. Surviving church dedications to them at Dunshaughlin (Dún Sechnaill, i.e. Secundinus), Killashee (Cell Auxilii), and elsewhere are all within a well-defined geographical area in the east and south-east, the area in which Christians were presumably most numerous and where Palladius would have based his ministry. It is therefore probable that Palladius's mission preceded that of Patrick by some decades; there is evidence to suggest that Patrick did not arrive until the late 450s.
It is unlikely that by the seventh century Irish scholars knew any more about Palladius than what was provided in Prosper's ‘Chronicon’. It is therefore improbable that there is any historical basis for the later traditions related in seventh- and eighth-century Patrician hagiography. This claims that Palladius was an archdeacon who brought relics of Saints Peter and Paul from Rome, that he had two disciples named Silvester and Solonius, that he was unable to make progress with the Irish mission, that he was martyred in Britain on his way home, in campo Girgin (identified as Fordoun in the Mearns), and that Patrick, on hearing of this, came post-haste from Gaul to continue where Palladius left off.
The early Irish church indeed believed that Christianity first came to Ireland from Rome. Columbanus (qv), writing to Pope Boniface IV in 613, stressed the orthodoxy of the Irish church, saying: ‘For all we Irish, inhabitants at the edge of the world, are disciples of Saints Peter and Paul . . . none has been a heretic . . . the catholic faith, as it was delivered by you first, who are the successors of the holy Apostles, is maintained unbroken’. The later traditions of Palladius were probably created and embellished in the course of Armagh's official promotion of Patrick as ‘national apostle’. The feast-day of Palladius is 7 July.