The foundation charter of the Royaumont Abbey was promulgated in 1228 and work began immediately. Louis IX bought land in the parish of Asnières-sur-Oise, at a place called Cuimont, which included mills and fisheries. In the foundation charter, written in Latin, Cuimont was renamed Mons Regalis, which was translated into French as Mont Royal and then Royaumont. The abbey of Royaumont thus became the 199th Cistercian abbey and the 21st daughter-abbey of Cîteaux. Louis IX negotiated with the Cîteaux Abbot the sending of 114 monks and 40 lay brothers. The name of the architect who built Royaumont remains unknown to this day.