Trier is a highly suitable place for Celtic studies because the city is situated in an area rich in archaeological monuments from the Hunsrück-Eifel and La Tène cultures (7th-1st c. BC) and the Roman period (1st c. BC - 5th c. AD). The district of the Treveri also played a significant role during the Gallic War (58–51 BC). In early medieval times, Irish scribes were at work in the scriptorium of Echternach. In the area between Hunsrück and Eifel, we find place names of Celtic origin in a number and density higher than one would expect.
Some traditions have it that a Celtic language still existed in the area in the fourth century AD. According to the famous testimony of the church father, St Jerome (347-420), Gaulish was still spoken at the time when he lived in Trier. To him, this clinging to the old way is nothing but "antiquated foolishness" (antiqua stultitia), but he also notes that the Galatians, whom he knew from his own experience, as well, "have almost the same language as the Treveri" (Galatas … propriam linguam eamdem pene habere quam Treviros, Commentariorum in Epistolam ad Galatas 357A, ed. Migne, Patrologia Latina, vol. 26). See T. Meißner, "Das Hieronymuszeugnis und der Tod des Gallischen", Zeitschrift für celtische Philologie 57 (2009/10), 107-112.
The illustration shows St. Jerome, depicted by Domenico Ghirlandaio (1449-1494).
Manuscript 137/50 (f. 48r–61v) in the City Library (Stadtbibliothek) of Trier contains the only fragment, originating from Ireland or an Irish monastery on the continent, of an Irish collection of the canonical law of the eighth century, the Collectio Canonum Hibernensis. This compilation was distributed all over Western Europe and is deemed to be one of the most important canonical collections of the early Middle Ages.
The Hibernensis was compiled around 735 AD by Rubin of Dairninis and Cú Chuimne of Iona. Their intention was to face the danger of differing interpretations of canonical rules and to prevent possible conflicts by a clear presentation of the law. A comprehensive analysis of the text is given by David Howlett: "The Prologue to the Collectio Canonum Hibernensis". Peritia 17/18 (2003/04): 144-149. Roy Flechner has presented a new complete edition: The Hibernensis, vol. I: A study and edition, vol. II: Translation, commentary, indexes, Washington D.C.: The Catholic University of America Press, 2019
The Trier fragment is a copy of the eighth century. However, the parchment was re-used in the eleventh century for a text from the "City of God" (De civitate Dei) by Augustine. On the illustration below, the original text can still be recognised to some degree.