The sector formed a discontinuous line about long along France's frontier with Italy, from the Aiguille des Glaciers on the Mont Blanc massif, through Bourg-Saint-Maurice to the Moulinière peak on the Massif des Cerces, to Valloire. The sector's fortifications barred the valleys and passes crossing the Alps, particularly the routes over the Little St Bernard Pass via the Tarentaise Valley and the Mont Cenis pass via the Maurienne valley.