Geometrical proposition rejected
departments (black borders) in 1791
The first French territorial departments were proposed in 1665 by Marc-René d'Argenson to serve as administrative areas purely for the Ponts et Chaussées (Bridges and Highways) infrastructure administration.
Before the French Revolution, France gained territory gradually through the annexation of a mosaic of independent entities. By the close of the Ancien Régime, it was organised into provinces. During the period of the Revolution, these were dissolved, partly in order to weaken old loyalties.
The modern departments, as all-purpose units of the government, were created on 4 March 1790 by the National Constituent Assembly to replace the provinces with what the Assembly deemed a more rational structure. Their boundaries served two purposes:
- Boundaries were chosen to break up France's historical regions in an attempt to erase cultural differences and build a more homogeneous nation.
- Boundaries were set so that every settlement in the country was within a day's ride of the capital of a department. This was a security measure, intended to keep the entire national territory under close control.
The old nomenclature was carefully avoided in naming the new departments. Most were named after an area's principal river or other physical features. Even Paris was in the department of Seine. Savoy became the department of Mont-Blanc.
The number of departments, initially 83, had been increased to 130 by 1809 with the territorial gains of the Republic and of the First French Empire. Following Napoleon's defeats in 1814–1815, the Congress of Vienna returned France to its pre-war size and the number of departments was reduced to 86 (three of the original departments having been split). In 1860, France acquired the County of Nice and Savoy, which led to the creation of three new departments. Two were added from the new Savoyard territory, while the department of Alpes-Maritimes was created from Nice and a portion of the Var department. The 89 departments were given numbers based on the alphabetical order of their names.
The department of Bas-Rhin and parts of Meurthe, Moselle, Vosges and Haut-Rhin were ceded to the German Empire in 1871, following France's defeat in the Franco-Prussian War. A small part of Haut-Rhin however remained French and became known as the Territoire de Belfort; the remaining parts of Meurthe and Moselle were merged into a new Meurthe-et-Moselle department. When France regained the ceded departments after World War I, the Territoire de Belfort was not re-integrated into Haut-Rhin. In 1922, it became France's 90th department. Likewise, the Lorraine departments were not changed back to their original boundaries, and a new Moselle department was created in the regained territory, with slightly different boundaries from the pre-war department of the same name.
The re-organisation of Île-de-France in 1968 and the division of Corsica in 1975 added six more departments, raising the total in Metropolitan France to 96. By 2011, when the overseas collectivity of Mayotte became a department, joining the earlier overseas departments of the Republic (all created in 1946) – French Guiana, Guadeloupe, Martinique and Réunion – the total number of departments in the French Republic had become 101. In 2015, the was split from Rhône to form the Métropole de Lyon, a sui generis entity, with the powers of both an intercommunality and those of a department on its territory, formally classified as a "territorial collectivity with particular status" (French: collectivité territoriale à statut particulier) and as such not belonging to any department. In 2018, the two departments of Corsica re-merged to form a single territorial collectivity (simultaneously region and department), reducing the number of departments to 100.