Sources: Bede, Ecclesiastical History of the English People (~731 AD); Adomnan, Life of Columba (~697 AD); Patrick, Confession (~450 AD); the Synod of Whitby (664 AD).

Celtic Christianity is the form of Christianity that developed in Ireland, Scotland, Wales, Cornwall, and Brittany from the 5th century onward — geographically and institutionally isolated from Rome during the turbulent migrations period, it developed distinctive practices and a spirituality that has exercised enormous romantic fascination in modern times. Distinctive features: (1) Monastic structure — Celtic Christianity was organized around monasteries rather than dioceses; the abbot, not the bishop, was the primary authority; the great monasteries of Iona (founded by Columba ~563 AD), Lindisfarne, Clonmacnoise, and Bangor were centers of learning and mission; (2) Easter date calculation — Celtic churches followed an older method of calculating Easter that diverged from Rome; this caused enormous controversy when Celtic missionaries met Roman Christians in England; (3) Tonsure style — Celtic monks shaved the front of the head (possibly following Druidic practice); Roman monks shaved the crown; (4) Illuminated manuscripts — the Book of Kells (~800 AD) and Lindisfarne Gospels are the artistic pinnacle of Celtic Christian culture; (5) Nature spirituality — Celtic theology had a strong sense of the divine presence in creation, the “thin places” (caol áit) where the boundary between sacred and material is permeable. The Synod of Whitby (664 AD) forced the Northumbrian church to choose between Celtic and Roman practices; Rome won, and the distinctive Celtic forms were gradually absorbed. Patrick’s Confession (~450 AD) is the earliest authentic personal document in British Christian history — a remarkable account of his captivity, escape, calling, and mission.