In a genealogy of the Mackenzies contained in The Black Book of Clanranald, we find it stated that Gilleoin of the Aird, from whom the old Earls Gillanders of Ross and the Mackenzies of Kintail are traced, was the son of Macrath (McRrath). Supposing the genealogy to be correct, this Macrath would have lived not earlier than the tenth century. By that time Christianity was fairly established in the Highlands of Scotland, and as the name Gilleoin means the servent of St. John, it is not at all unlikely that Macrath also may have been so named from some family connection with the early Church in the Highlands.
In a Gaelic MS. of 1450, containing genealogies of several Highland families, and published with an English translation in The Transactions of the Iona Club, an ancestor of the Macleans is also mentioned as Gilleoin, son of Macrath (Gilleain me Icrait). This helps to confirm the tradition mentioned below, that the Macraes, Mackenzies, and Macleans were of the same ancestry, but it is not easy to make anything satisfactory out of those old genealogies.