The site, which is about two miles outside the town, on the Kilcullen Road, has always been associated with a foundation by St Auxilius, nephew of St Patrick.
Auxilius seems to have been important in the early Irish Christian church and there is a reference to a Synod of Bishops being held in 448 or 450, headed up by Patrick, Auxilius and Isserninus. This would seem to suggest that he had some special eminence or authority among the bishops, for the laws made there would have been binding on the whole Irish church at the time.
Both the annals of Innisfallen and Clonmacnoise give 458 A.D as the date when this famous cleric died but there is some disagreement over when his feast day was celebrated, with one source giving 19 March (just two days after the feast day of his more famous uncle) and another giving 27th August as the date.
The foundation would seem to have flourished, even after Auxilius’ death, and the names of two further early Abbots of Killashee are known from the annals.
By the ninth century however, the foundation – like other religious sites in Ireland – became subject to the depredations of Viking marauders and there is an account of its destruction in 824 and, indeed, again in 1035.
Today, all that remains on the site is the shell of a church of Ireland church (closed in 1965) which may contain some elements of an earlier medieval church and having an intriguing ‘Round Tower’ attached to its west end, a surrounding ancient graveyard and a nearby ‘Holy Well’ dedicated to St Patrick.
Up until recent years, the latter was still visited, on St Patrick’s Day, by parishioners of the Two Mile House parish, thus maintaining an ancient line of tradition of religious worship at Killashee. Sadly, this practice now seems to have been discontinued.