Adam Marsh, or Adam de Marisco (mâr´Ĭskō), d. 1259?, English Franciscan scholar. He was a student of Robert Grosseteste. When Grosseteste became bishop, Marsh took his place in the Franciscan school at Oxford. Marsh's advice and his services as a peacemaker were constantly sought, and Grosseteste relied heavily on him. Actively supporting the reform party of Simon de Montfort (1208?–1265), Marsh was able nevertheless to retain the confidence of Henry III. Of his writings only his letters survive.