The origins of Montreuil, whose name derives from the Latin 'monasteriolum' (small monastery), are closely linked to its religious history.
The abbey church of Saint-Saulve in Montreuil-sur-Mer was built in the 12th century and is located on the site of an older monastery dedicated to Saint Walloy, founded in the 10th century.
In 926, the monks of Landévennec (Finistère) fled the Norman invasions and found refuge in Montreuil, where they founded the abbey of Saint-Walloy (local deformation of the name Saint Guénolé). In 1111, this abbey changed its name when the remains of Saint-Saulve were brought there.
In its original design, the building had a layout typical of pilgrimage churches with an ambulatory and radiating chapels.
In the Middle Ages, the numerous relics attracted pilgrims to Montreuil and gave the town a character of holiness. It was then nicknamed 'The Necropolis of Ponthieu'.
The reconstruction after the earthquake of 1467 caused the collapse of at least six religious buildings, including the Hôtel-Dieu and the Saint-Saulve church, which was completely rebuilt at the beginning of the 16th century.