Brought up a Christian, St. Patrick was captured by Irish pirates at the age of 15 and sold into slavery. Seeking ordination, he escaped Ireland to train in Britain, returning to Ireland as a bishop in about 432. Ireland was the only place in western Europe besides Caledonia (modern Scotland) that had never been conquered by the Romans. It had therefore preserved its pagan gods, its particular law system, its own economy, and its own language. Patrick's mission there was not the first time Christians had worked to spread the gospel, but for 30 years he established local churches and monasteries as centers of the new Christian faith, which the Irish were swift to embrace.
Price, Matthew and Michael Collins. The Story of Christianity: 2000 Years of Faith. Wheaton: Tyndale House Publishers. 1999. 79