At Saint-Martin-d’Hardinghem, in advance of the construction of flood retention basins in the Aa river valley, Inrap excavated, in partnership with the Department of Pas-de-Calais, part of the country residence of the bishops of Thérouanne, dated to the High Middle Ages. The archaeologists uncovered 200 m² of decorated pavements, all of which are very well preserved, which is rare.