The Massif has a perimeter of approximately one hundred and twenty miles and its rock face rises impregnable and sheer as a fortress to three thousand feet, and it dominates the departements of the Drôme and of Isere.
Seven narrow roads only form a tracery of navigable highways out in the rock, and tunneled through, it.
A sequence of gorges, their walls lofty and abrupt, their depths noisy with rapids and waterfalls, split the Massif in two. They are distinct, autonomous areas, militarily speaking : the North Zone and the South Zone.
The defence of this natural citadel rested largely on bluff. The interior was left undefended. The Maquis were able to place a man armed with a rifle or a machine gun every half mile along the boundary, each man separated from his neighbour by airy ravines, torrents, woods and other natural obstacles.
That day there were two hundred men to defend the Massif. The local Resistance headquarters proclaimed the Germans would be repulsed, if they numbered less than twenty thousand.