https://en.wikipedia.org/wiki/Subprefecture
A subprefecture is the administrative town of an arrondissement where an arrondissement does not contain the prefecture.The civil servant in charge of local executive power is the sous-préfet.. Examples: Aix-en-Provence, Apt, Arles, Bayonne, Boulogne-Billancourt, Boulogne-sur-Mer, Calais, Cambrai, Chalon-sur-Saône, Château-Thierry, Cherbourg, Le Havre, Narbonne, Reims, …