Even after the death of Saint Louis in 1270, the Royal Abbey of Royaumont enjoyed the aura of its founder. But its decline began with the Hundred Years’ War (1337-1436). Initially spared by the exactions of the English, the abbey was ransomed and devastated several times. At the beginning of the 15th century, Royaumont was very weakened, like all Cistercian abbeys. The number of monks had fallen and would never again exceed 25. In 1549, the abbey was given in commendation to personalities close to the royal power, such as the Lorraine family or Cardinal Mazarin, who never set foot there. At the time of the Revolution, there were only 10 monks left.