 Mack decided to make the city of Ulm the centerpiece of his defensive strategy, which called for a containment of the French until the Russians under Kutuzov could arrive and alter the odds against Napoleon.Ulm was protected by the heavily fortified Michelsberg heights, giving Mack the impression that the city was virtually impregnable from outside attack.Fatally, the Aulic Council decided to make Northern Italy the main theater of operations for the Habsburgs.