"Saint Patrick's Breastplate" is an Old Irish prayer of protection of the "lorica" type (hence "Lorica Sancti Patricii", or "The Lorica of Saint Patrick") attributed to Saint Patrick. Its title is given as Faeth Fiada in the 11th-century Liber Hymnorum that records the text. This has been interpreted as the "Deer's Cry" by Middle Irish popular etymology, but it is more likely a term for a "spell of concealment". It is also known by its incipit (repeated at the beginning of the first five sections) atomruig indiu, or "I bind unto myself today". The prayer The prayer is part of the Liber Hymnorum, an 11th-century collection of hymns found in two manuscripts kept in Dublin. It is also present, in a more fragmentary state, in the 9th-century Vita tripartita Sancti Patricii. It was edited in 1888 (Vita Tripartita), in 1898 (Liber Hymnorum), and again published in 1903 in the Thesaurus Paleohibernicus. The Liber Hymnorum gives this account of how Saint Patrick used this prayer: Saint Patrick sang this when an ambush was laid against his coming by Loegaire, that he might not go to Tara to sow the faith. And then it appeared before those lying in ambush that they (Saint Patrick and his monks) were wild deer with a fawn following them. The description concludes "fáeth fiada a hainm", which was interpreted as "Deer's Cry" by the medieval editor of the Liber Hymnorum (hence the connection to the deer metamorphosis), but the Old Irish fáeth fiada properly refers to a "mist of concealment". The prayer as recorded is dated on linguistic grounds to the early 8th century. John Colgan (1647) attributed the prayer to Saint Evin, the author of the 9th-century Vita Tripartita. It was also Colgan who reported the title of Lorica Patricii. Christian in content, it shows pre-Christian influence. Because of this it is also known as the "Lorica of St. Patrick" or as "St. Patrick's Breastplate". The term Lorica is used of a number of Old Irish prayers, including one attributed to Dallán Forgaill and another to Saint Fursey. They all arose in the context of early Irish monasticism, in the 6th to 8th centuries. It isn't clear when the Latin title of Lorica was first applied to them, but the term is used in the 17th century by John Colgan. The allusion is probably to Ephesians 6:14, where the Apostle bids his readers stand, "having