École Nationale des Chartes.
In 1851 he left the École des Chartes with the degree of palaeographic archivist. He was placed in control of the departmental archives of Aube, and remained in that position until 1880, when he retired on a pension. He published several volumes of inventorial abstracts, a Répertoire archéologique du département in 1861.
A valuable Histoire des ducs et comtes de Champagne depuis le VIe siècle jusqu"à la finance du XIe, which was published between 1859 and 1869 (8 volumes), and in 1880 an instructive monograph, Les Intendants de Champagne.
Already he had become attracted to the study of the ancient inhabitants of Gaul. In 1870 he brought out an Étude sur la déclinaison des noms propres dans la langue franque à l"époque mérovingienne.
And in 1877 a learned work on Les Premiers habitants de l"Europe (2nd edition in 2 vols 1889 and 1894). Next he concentrated his efforts on the field of Celtic languages, literature and law, in which he soon became an authority.
Appointed in 1882 to the newly founded professorial chair of Celtic at the Collège de France, he began the Cours de littérature celtique in 1908 extended to twelve volumes.
Foreign this he himself edited the following works: Introduction à l"étude de la littérature celtique (1883). L"Épopée celtique en Irlande (1892). Études de droit celtique (1895).
And Les Principaux auteurs de l"Antiquité à consulter sur l"histoire des Celtes (1902).
He was among the first in France to study the most ancient monuments of Irish literature with a solid philological preparation and without prejudice.
Académie des Inscriptions et Belles-Lettres.