The large moat behind the fort has been turned into a marina for boats , the Bassin de l'Arsenal . To the north , a covered canal , the Canal Saint Martin , goes under the road along the edge of the site . The large ditch ( fossÃ ) behind the fort has been transformed into a marina for pleasure boats , the Bassin de l'Arsenal , to the south , and a covered canal , the Canal Saint Martin , extending north from the marina beneath the vehicular roundabout that borders the location of the fort .