The Allies had had time to consider the problem. The French being brought around to agree that the key to the defence was the Malakoff.:441 Emphasis of the siege at Sevastopol shifted to the British left, against the fortifications on Malakoff hill.:339 In March, there was fighting by the French over a new fort being built by the Russians at Mamelon, located on a hill in front of the Malakoff. Several weeks of fighting saw little change in the front line, and the Mamelon remained in Russian hands.

What did the French believe was instrumental in their defense?