[2] In 823, in co-operation with Bishop Artrí mac Conchobar of Armagh, he had the "Law of St. Patrick" established in Munster,[3] and sacked the monastery, that of Gailline of the Britons, in modern County Offaly.
[6] In 830, Fedelmid was back burning monasteries--this time it was probably that of Fore Abbey in modern County Westmeath,[7] while in Southern Galway, he destroyed the Uí Briúin,[8] and in the same year, the Munstermen were recorded as killing Folloman, son of Donnchad, brother of Conchobhar, the High King of Ireland.
[9] In 831 and 832, he is recorded as taking an army of Leinster and Munster into East Meath, plundering as far north as Slane,[10] while also raiding the Dealbhna Beatha of southern Offaly three times, and burning Clonmacnoise.
The year 840 was probably the high point of Fedelmid's rule, when he ravaged the east midland kingdoms of Mide and Brega and is recorded as having rested in Temhar (Tara), and the annals have a short poem on this:Feidhlimid is the King, To whom it was but one day’s work [To obtain] the pledges of Connaught without battle, And to devastate Midhe.
The Annals of Clonmacnoise offer the following description:After his returne to Munster ye next year, he was overtaken by a great disease of the flux of the belly, which happened in this wide.