The Maginot line defenses – up to deep from the forward positions to the rear line – were intended to prevent a surprise attack and delay any attack while the French Army was mobilized. With the relative numerical inferiority between the France and Germany, it was a more effective use of manpower. Within the line, passive anti-tank obstacles were supported by anti-infantry and anti-tank bunkers. After Belgium declared neutrality in 1936, France began work on extending the line along the Belgian border.