Religion in the Republic of Ireland
The predominant religion in the Republic of Ireland is Christianity, with the largest church being the Roman Catholic Church. The Irish constitution says that the state may not endorse any particular religion and guarantees freedom of religion.
Gaelic Ireland
The introduction of Christianity to Ireland dates to sometime before the 5th century, with Palladius (later bishop of Ireland) sent by Pope Celestine I in the mid-5th century to minister to Irish "believing in Christ". Early medieval traditions credit Saint Patrick as being the first Primate of Ireland. Christianity would eventually supplant the existing pagan traditions, with the prologue of the 9th century "Martyrology of Tallaght" (attributed to author Óengus of Tallaght) speaking of the last vestiges of paganism in Ireland.