This is a Cistercian abbey founded by king of France saint Louis. He bought an estate called Cuimont from Benedictine friars of Saint-Martin de Boran. He gave it the name of "royal monastery", regalis mons.
The first buildings were finished in 1228, then saint Louis called some Citeaux monks. In October 1235, the archbishop of Mitylène, Jean, consecrated the church dedicated to the Virgin Mary. The king gave some money for monks' wages.
King saint Louis came very often in his abbey: he lived among the monks, took dinner with them. He also brought relics of Holy crown of thorns, of Thomas Canterbury and saint Agnes. Royaumont became very important.
King's brothers and children were buried in the abbey. It was devastated during the Hundred Years War, then burnt by a fire in 1760. It was sold in 1791 to the marquis de Travannet who demolished it one year later.
Saint Louis biographer, Guillaume de Saint-Pathus, told the king took his dinner with the monks; he served them himself. One day, Louis dirtied himself by spilling some sauce on his clothes, as he ate at the abbot's table. This one told him to be careful, because his cloak was stained. Louis answered: "I don't care, I have others!"
The king took part in the building works, he even took a bed on the monk's dormitory. He came to cure sick persons at the infirmary. Louis was also very generous with Royaumont, he gave it lands, food and his protection.