Dáibhí Ó Cróinín writes that "The Fothairt were the original population group around the site of Bridgit's monastery at Kildare" (p. 197), further stating that the Uí Ercáin, a branch of the Uí Meic Cruaich (a sub-sept of the Fothairt) "are remembered in the 'Vita Tripartia' as having been specially favoured by Patrick, who blessed them (Dobert Pátraic bendachtain ... for Uu hErcá huili) and their king, Fergnae mac Cobthaig, who is also mentioned in the life of Fintan/Munnu of Tagmon, where he encounters the saint in campo Lyffi ('in the Liffy plain')."
The kingship of Leinster was held from the mid-8th century to 1042 by the Uí Dúnlainge, who bolstered their early gains "by means of political marriage with Sárnat, daughter of Eochu mac Baíth of the Fothairt" (p. 197).
In addition, two kings of Forthairt, Fergus mac Móenaig and Dub dá Chrich mac aui Cellaig mec Triein, "as well as 'many others, omitted for the sake of brevity'", were killed at the battle of Ath Senaig (Ballyshannon, near Kilcullen, County Kildare) in 738 as supporters of King Áed of Leinster (p. 200).
Despite their political eclipse, the Fothairt "continued to supply leading clergy to Kildare.
And it is highly probable that many other Kildare clerics, whose origins cannot be established with certainty, belonged to Fotharta."