The greater part of the district is occupied by a semicircle of heights (from 650 to 1000 ft. in height) stretching from Moulins-la-Marche on the northwest to Montmirail on the south; within the basin formed thereby the shape of which is defined by the Huisne, an affluent of the Sarthe, lie the chief towns of Mortagne-au-Perche, Nogent-le-Rotrou and Bellême.