The abbey was founded in 557 by Clotaire I on his manor of Crouy, near the villa of Syagrius, just outside the then boundaries of Soissons to house the remains of Saint Medard, the legend being that during the funeral procession the bier came to a standstill at Crouy and was impossible to move until the king had made a gift of the whole estate for the foundation of the abbey.
In accordance with Salian tradition, the kingdom was divided between Clovis's four surviving sons: Childebert I in Paris, Chlodomer in Orléans, and Clotaire I in Soissons.