OG Donnán, St Donnan
St Donnan, who is commemorated at Cill Donnain / Kildonan is in some ways the most important saint commemorated in Uist for our chances of understanding the nature of early Christianity there. This is because for Donnan we have a clear understanding of when and where he worked, historically, and also some detailed evidence for the cult of Donnan as a martyr saint in the years after his death.
St Donnan is inextricably associated with the island of Eigg, where he was abbot of a monastery in the early seventh century. He was roughly contemporary with Columba, to whom he is linked in a number of late, improbable legends. He was killed, along with a very large number of his monks (numbers range between 52 and 150), and their monastery burned: the Annals of Ulster describe this (‘combustio martirum Ega’) under the year 617, but the correct AD date is likely to be 619, and so the 1400th anniversary of St Donnan’s death will take place in 2019. The names of many of his monks are recorded in the 9th-century Martyrology of Tallaght : there is little reason to doubt this list as being of his monks (see Clancy 2015 for discussion) . The site of the monastery is almost certainly where Kildonnan (Canmore ID 22152) in Eigg is now.
Although we have legends from at least the 12th century depicting the massacre as instigated by the local (female) landowner, unhappy about Donnan grazing his sheep on her land,  we have no further contemporary record of Donnan. However, the fact that Donnan’s monastery was probably beyond the bounds of where Gaelic-speakers lived and ruled in western Scotland has allowed historians to speculate that the massacre was fuelled by anti-Christian sentiment from still pagan Picts.  Whether caused by religious or land tensions, it is clear that Donnan’s monastery was very heavily populated by Gaels, in an area which was probably Pictish at the time. This would reflect the situation in contemporary Uist as well.
The massacre was not the end of the monastery--it either continued or was re-founded at some point, since we hear about later personnel in 725 and 752 . The Martyrology of Tallaght (dating from c.830, but based on older sources) also commemorates a series of saints from Eigg, almost certainly later abbots: Conán, Berchán, Congalach. The reason we know about all this is probably that Donnan was being particularly venerated in Iona. Iona lies behind the annals as found in the Annals of Ulster and also behind the Martyrology of Tallaght.  It is probably Iona who had a particular interest in Donnan as a sort of universal martyr, which contributed to his later popularity.
There a number of dedications to Donnan in the Hebrides, that at Cill Donnain in Uist being one, along with Skye and Lewis, and several on the adjacent mainland, for instance at Loch Broom. Almost all of these take the form Cill Donnain / Kildon(n)an. We know that Donnan lived, worked and died at a monastery at what is now Kildonnan on Eigg--but we are not therefore able to say that he was present at any of the other places that bear his name. For very many of them--especially in south-west Scotland--we are probably instead seeing the result of his cult as a martyr-saint in the centuries after his death. Cill Donnain reflects the cult of Donnan as a saint, it does not in itself tell us that he was ever there, and more than Cill Pheadair tells us St Peter was in Uist.
That said, it is unquestionable that Uist was, at the time of Donnan’s death, in the same cultural zone as Eigg (the two islands are intervisible in the right weather), and we cannot rule out the possibility that Donnan, and his monks, were historically active on Uist. Like Eigg, and like Skye (where we are told Columba needed an interpreter), Uist around AD 600 was probably Pictish-speaking, and Pictish stones from Benbecula and Pabbay, Barra (see Fisher 2001) reinforce South Uist as cultural Pictish. It was also likely not yet Christianised, or not to any strong degree, to judge from the continuity into the 8th century of non-Christian burial practices as seen at Cille Pheadair . The roll-call of Gaelic names among the dead monks of Donnan’s monastery on Eigg makes the forceful point that Christianity and Gaelic often went hand in hand as they expanded north in the West Highlands and Islands.
Donnan was commemorated particularly as a martyr, one of the very few Gaelic saints to suffer so-called “red martyrdom”. As noted, the Martyrology of Tallaght associates Donnan with other martyr saints, in a peculiar feast day on 17th April:
Zephán 7 Lurint 7 Geurgii 7 na naidin i mBethil 7 Petar decoin 7 Donan Ego co n-ulib martirib in domuin hoc die commemorantur,
“Stephen and Lawrence and George and the babies in Bethlehem, and Peter the Deacon, and Donnán of Eigg, with all the martyrs of the world, on this day they are commemorated.”
Three days later, on 20th April, these martyrs are celebrated again , this time probably commemorating the translation of their relics:
Communis sollemnitas omnium sanctorum et vriginum Hiberniae et Britanniae et totius Europae et specialiter honorem sancti Marini episcopi, et familae Ego elivatio.
‘The communal solemnity of all the saints and virgins of Britain and Ireland and Europe and especially to the honour of the holy bishop Martin [of Tours], and the elevation of the monastic community of Eigg.’
We find Donnan mentioned among collections of relics--in an Old Gaelic poem (perhaps of the eighth century) which lists Donnan’s knee-cap among many other items; and in a recently discovered list of relics of Irish saints, possibly from the 7th or 8th century, described by Julia Smith , where the relics of Donnani martiris are mentioned along with those of many other early Gaelic saints.
His status as a martyr may not entirely explain the distribution of churches commemorating him. It has been suggested that Donnan was taken up as a saint by the Scandinavians when they settled in the Hebrides, as what can be called an “expiation cult”: in other words, Donnan died the sort of death Vikings had inflicted on many monks and monasteries, and so repentant and newly Christian Vikings turned to him as their patron. There is a good parallel for this, in the cult of St Edmund in England—martyred by Vikings in 869, but mere years later commemorated in Christian coinage as a saint by Scandinavian rulers in England, and later venerated especially by the Danish king of England, Cnut.
Later legends depict a sort of rivalry between Columba and Donnan. The 14th-century Leabhar Breac gives us this anecdote:
This Donnan is he who went to Columcille, to take him for his confessor (anamchara, lit. “soul-friend”). And Columcille said to him, ‘I will not be a confessor,’ said he, ‘to people who are to suffer violent martyrdom; for thou shalt enter violent maryrdom, and thy community with thee.’ And that is what was fulfilled. Donnan went after that among the Gall-gaidil, and took up his abode in the place where the queen of the country’s sheep used to be. This was told to the queen. ‘Kill them all’, said she. ‘That is not devout’, said the others. Thereafter men go to them, to kill them. The priest was then at mass. ‘Grant us peace till the mass is ended,’ said Donnan. ‘We will’, said they. Thereafter they were all killed, as many as were there.
But this is a late legend. It is too flimsy to build on, as some have done, seeing Donnan and his cult in the Hebrides as a sort of contra-Columba.  Rather, it may well be Iona itself which cultivated Donnan’s memory on Uist, and helped to keep it alive during the Viking age.