Most of them were created during the first Christianization of Gaul, in the 3rd to 5th centuries.[citation needed]
But, at several occasions during the Middle Ages or the Ancien Régime, new dioceses were created, replacing older ones or carved out of them. For instance, the Albigensian Crusade entailed the creation of many new dioceses in the early 14th century. All the same, in 1789, on the eve of the French Revolution, the ecclesiastical map of France still very much recalled that of Roman Gaul. This explains why many dioceses and provinces did not coincide with French borders, with their head cities lying in present-day Belgium, GermanyorSwitzerland.
In 1790, this map was entirely revised to fit the new administrative map: dioceses were now to coincide with départements (the new administrative units). Ancien Régime dioceses all disappeared, then, in 1790. Many former bishoprics remained heads of the new dioceses, but many cities lost their bishop. Even so, in those cities, the former cathedral very often kept its rank as a cathedral church. This explains why many post-Revolutionary episcopal sees bear the name of several cities. For instance, in the département of the Drôme, only the city of Valence retained its bishop, the former episcopal sees of Die and Saint-Paul-Trois-Châteaux being suppressed, but the bishop retained the title of bishop of Valence, Die and Saint-Paul-Trois-Châteaux.
Here follows a list of Ancien Régime dioceses, as of 1789, on the eve of the Revolution. With the exception of those dioceses which were created in the Late Roman period (before the 6th century), whose date of creation generally cannot be established, we provide the date of creation and, when appropriated of suppression of the bishopric. Dioceses whose sees were not within the borders of the kingdom of France are in brackets.
