In the spring of 1800, Napoleon and his troops crossed the Swiss Alps into Italy, aiming to surprise the Austrian armies that had reoccupied the peninsula when Napoleon was still in Egypt. After a difficult crossing over the Alps, the French army entered the plains of Northern Italy virtually unopposed. While one French army approached from the north, the Austrians were busy with another stationed in Genoa, which was besieged by a substantial force. The fierce resistance of this French army, under André Masséna, gave the northern force some time to carry out their operations with little interference.