16Jackson, Kenneth Hurstone. The Oldest Irish Tradition: A Window on the Iron Age. Cambridge: Cambridge UP 1964. 46.
As Walter Johnson observed, medieval clergy often expressed an interest in the excavation of prehistoric burial barrows, believing them to contain the bones of early Irish saints. "...we may infer that even the mediaeval churchmen imputed sanctity to barrows, although the belief found expression in paradoxical acts of desecration." (Johnson, Walter. Byways in British Archeology. Cambridge: Cambridge UP, 1912. 82-3.)
Also, note the story of the conversion of the three pagan princesses at the Ogulla Well of Rathcroghan.