The Irish people in ancient times were polytheistic, worshipping gods and goddesses of Celtic origin. When Christianity came to Ireland from Roman Britain, the Irish developed their own regional expression of the religion. The Anglo-Norman invasion enforced greater conformity to Catholic standards, and the adoption of Protestantism by Ireland's English rulers brought the Reformation to Ireland. Presbyterian and Anglican settlers established a Protestant tradition, leading to centuries of conflict with Irish Catholics.
The pre-Christian Irish worshipped a pantheon of deities called the Tuatha De Danann. The Tuatha De Danann included the war goddesses Badb, Macha and Nemain, a divine king named Nuadu of the Silver Hand, Lug of the Long Arm who defeated the sinister Balor, a father god named the Dagda or "the good god," and the Dagda's children Oengus the god of youth and Brigit the goddess of poetry, healing and smithcraft, along with many other deities of varying importance.
Early Irish Christianity
Christianity came to Ireland sometime in the fourth or fifth century, when Irish warriors were raiding Roman Britain and taking Christians back to Ireland as slaves. By 431, enough Christians were living in Ireland for Pope Celestine to send them a bishop, a man named Palladius about whom little is known. St. Patrick was in Ireland as a missionary sometime later that century, and the number of Christian converts continued to grow until the pre-Christian religion disappeared. By the seventh century, Irish economic and intellectual activity was centered around a network of Christian monasteries, which then became the focus of attacks by Viking raiders. Although early Irish Christianity was not radically different from Christianity elsewhere in Europe, the Irish monasteries tended to be conservative about adopting new ideas like the Benedictine and Cistercian monastic reforms.
The Norman Invasion
Beginning in the 12th century, Norman warriors from England began to invade and conquer sections of Ireland. The Anglo-Normans had the support of Pope Adrian IV -- a fellow Englishman -- who wanted to bring the Irish church in line with Catholic practices elsewhere, and who believed Irish Christianity had absorbed too many pagan influences. The Anglo-Normans never succeeded in conquering the whole island, so the church in Gaelic or native Irish areas remained distinct from the church in areas under English control.
When the English King Henry VIII established the Church of England, the areas of Ireland under English control became part of the Protestant Church of Ireland. Queen Elizabeth I succeeded in extending English rule over most of the island, and loyalty to the Catholic faith became a symbol of Irish opposition to English rule. From 1603 onward, the English government encouraged Protestants from England and Scotland to establish colonies in the northern Irish province of Ulster.
Catholic and Protestant
In 1641, Catholic rebels tried to drive the Protestants out of Ulster, but did not succeed. When the Irish Catholics backed the Stuart monarchs of England in their civil war with Parliament, the English Protestant ruler Oliver Cromwell invaded from 1649 to 1650. Protestant King William of Orange defeated the Stuart forces in Ireland in 1689, and from 1690 onward Catholics were disenfranchised by law in Ireland. The law also favored followers of the Church of Ireland over Presbyterians, so some Presbyterians joined the Catholic rebels of 1798 in fighting for Irish independence. After the failure of the uprising, Irish Protestantism of all kinds became increasingly associated with loyalty to British rule, while Catholicism remained associated with Irish nationalism.
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