It is often not appreciated even today by many genealogists that some of the late medieval Irish genealogies are clever and sometimes not so clever forgeries. However, the influence of these forgeries continues to be very widespread, often with many people who should know better.
The best example to deal with first is a Donegal family that I have often spoken about before in my blogs ~ the McSweeneys. Everyone accecpts that the McSweeney galloglasses originally came to Ireland from western Scotland, during the period of the Scottish Wars of Independence that were fought in the early decades of the 1300s. However, it is not so well known that once the McSweeney families became powerful in County Donegal and also in many other parts of Ireland, that the late medieval Irish genealogists constructed an elaborate forged genealogy for them, stating that the family were descended from Aodh Athlomhan O'Neill, a king of Tyrone who died in the year 1033. The legend goes that Aodh had two sons, the elder Domhnall and the younger Anradhán. When the father died, Anradhán illegally seized the kingship of Tyrone, but was deposed by his elder brother, who then cursed Anradhán and his followers. As a result Anradhán and his men left Ireland for Scotland where they settled, and where three generations later their descendant Suibhne, who lived around the year 1200 was born. This is a good story but it is not in anyway true. None of the older Irish genealogies contains any reference to Domhnall and Anradhán O'Neill, nor do any of the Irish annals. Real evidence for the origin of the McSweeney family is however preserved in the Scots Gaelic bardic poem 'Dál Chabhlaigh ar Chaisteál Suibhne ~ A Meeting of a Fleet Against the Castle of Suibhne', which was composed by Artúr Dall Mac Gurcaigh around the year 1300. This poem refers to the McSweeneys as 'Lochlannigh is ármuinn iad ~ they are Norsemen and brave chiefs'. However, the false legend of descent from the O'Neills has corrupted all the late medieval and early modern collections of Irish genealogies which accept unquestioningly the fabled descent from Anradhán O'Neill.
There is a similar story connected with the other most famous galloglass family in Ireland the McDonnells, although in this instance the forgery is 'awkward and unconvincing'. The McDonnells are descended from the great Scottish chieftain Sumarlidi or Somhairle in Irish, who founded the Kingdom of the Hebrides in the mid twelfth century. Although Somhairle was a Gaelicized chieftain and ousted Norwegian influence from the islands to the west of Scotland, no one doubts his ultimate descent from Norse settlers in the Isles. The McDonnells were related to Somhairle's family and this fact is recognised in some of the older Irish medieval genealogies. However, again when the McDonnell galloglass family became powerful in Ireland during the 1300s the late medieval Irish genealogists attempted to forge a fictional descent from the entirely seperate and wholly Irish minor McDonnell family of Clankelly in Fermanagh. Although, as I have already stated this fabrication was not as sophisticated as the McSweeney forgery, the forged McDonnell galloglass origin legend in the words of one modern Irish historian has still 'tainted every MacDonald genealogical document', since then. This can be quite serious when modern historians or genealogists accept unquestioningly these late medieval forgeries, especially when they incorporate them into published work which only preserves and prolongs the forgeries.
There are quite a few more examples that I could give. But to conclude, I will just describe one more forgery, which again concerns the famous O'Neill family of Tyrone. This time the family in question is surprisingly the McLoughlins, who were probably the second most important Tyrone Royal family, who provided most of the kings of Tyrone from about 1050 AD to 1200 AD, and who include two high-kings of Ireland (Domhnall McLoughlin and Muirchertach McLoughlin), amongst their distinguished number. Uncorrupted medieval Irish poetry and some genealogical material record the descent of the McLoughlin family from a man called Domnall Dabaill, a king of Tyrone who died in the year 915. For whatever reason the later medieval genealogists forged a descent for the McLoughlins from Domnall's brother Niall Glúndub, a high-king of Ireland who died in 919, who was the ancestor of the O'Neill family. Obviously this was done in late medieval times when the McLoughlins fell from power and the O'Neills were kings of Tyrone and perhaps the most famous and powerful family in all of Gaelic Ireland. The example clearly shows I think how senses of prestiege and likely attempts to please patrons corrupted some of the late medieval Irish collections of genealogies. Also when only historical accuracy and truth were hurt in a process which probably pleased a lot of influential people in late medieval Ireland, the lure and appeal of genealogical forgery can perhaps be understood. I do hope however that any genealogists who read this blog will take on board the warning to beware of some of the genealogical material that survives from late medieval Ireland.