Liber Hymnorum

The Liber Hymnorum is the medieval Irish manuscript collection compiled by anonymous Irish scribes that preserves the Deer's Cry, also known as Saint Patrick's Breastplate, together with a prefatory legend explaining its supposed origin. The hymn's Old Irish language belongs to roughly the eighth century, some three centuries after Patrick's own lifetime, so the collection preserves the poem rather than an eyewitness record of its composition. Its strength is that it is the primary manuscript witness for a text otherwise known only through later copies and translations, and its own linguistic evidence is what lets scholars date the poem independently of its attributed author. Its limit is that the attribution to Patrick himself is the prefatory legend's claim, not something the hymn's own language can confirm, so a claim of Patrician authorship should be presented as traditional attribution rather than established fact.