Mauvoisin

The Mauvoisin were a feudal family of the French royal domain, rooted around Rosny-sur-Seine on the Normandy border. The first known lord, Raoul Mauvoisin, held Rosny and the viscounty of Mantes and died after 1074; his raids into Evreux helped provoke William the Conqueror's campaign of 1087, which ended with the destruction of Mantes.

As vassals of the Capetian kings the family made its name in arms. Pierre fought for Philip Augustus at the Battle of Bouvines and received the lordship of Nonancourt, while Guy IV followed Louis IX to Taillebourg and the disaster of Al Mansurah in 1250.

Its prelates included Samson, archbishop of Reims from 1140 to 1161. In 1337 the family still held castles between the Seine and the Norman frontier; the house became extinct in 1458.