Prior to the arrival of the Normans, much of what is now eastern County Offaly was under the control of the O’Conor Faly clan. The invaders pushed them west, their lands granted to the knight Robert de Bermingham who had participated in Henry II’s expedition to Ireland in 1172. However, over the next 100 years the O’Conor Faly’s gradually returned to their former territory and in 1294 they captured Kildare Castle. By then their opponent was de Bermingham’s descendant Piers Mac Feorais, Baron of Tothemoy who in 1289 had been appointed by the crown authorities to guard the much of the frontier in Kildare. Finally in 1306 a truce was reached between him and Mac Feorais agreed to act as god-father to the nephew of Murtough O’Conor Faly, then head of the clan.

On the Feast of the Holy Trinity, 1306 the Berminghams and the O’Conor Falys gathered for the baptismal ceremony at Carrickoris church, and then adjoined for a feast at the adjacent feast. However, as the Annals of the Four Masters later recorded, ‘O’Conor Faly (Murtough), Maelmora, his kinsman, and Calvagh O’Conor, with twenty-nine of the chiefs of his people, were slain by Sir Pierce Mac Feorais Bermingham in Mac Feorais’s own castle, by means of treachery and deceit.’ The little godson meanwhile was thrown off the top of the battlements and so died. Now wonderfully peaceful, this is the site, if not the actual building, where the notorious massacre took place.