From Wikipedia

The Siege of Leningrad

The Siege of Leningrad, also known as
The Leningrad Blockade  was an unsuccessful military operation by the Axis powers to capture Leningrad (now Saint Petersburg) during World War II. The siege started at 9 September 1941, when the last land connection to the city was severed. Although Soviets managed to open a narrow land corridor to the city at 18 January 1943, the total lifting of the siege happened at 27 January 1944, 872 days after it began. The Siege of Leningrad was one of the longest and most destructive sieges of major cities in modern history and it was the second most costly in terms of casualties.

The capture of Leningrad was one of three strategic goals in Hitler's initial plan, codenamed Operation Barbarossa, for invading and conquering the Soviet Union. Hitler's strategy was motivated by Leningrad's political status as the former capital of Russia and the symbolic capital of the Russian Revolution, its military importance as a main base of the Soviet Baltic Fleet and its industrial strength, housing numerous arms factories.

Hitler was so confident of capturing Leningrad that invitations to the victory celebrations to be held in the city's Hotel Astoria were already printed. Although Hitler's plan for taking the city failed, the two-and-a-half year siege caused the greatest destruction and largest loss of life ever known in a modern city.

The siege was conducted by Wehrmacht troops associated with Army Group North, with assistance from the Finnish Army, as part of Barbarossa, which was launched on 22 June 1941. The siege followed the Finnish offensive in Karelia, and the German offensive on southern suburbs of Leningrad. Once the offensive portion stopped and the 4th Panzer Group had left for Moscow, the Germans started to dig in as a preparation for executing the siege. General Georgy Zhukov overlooked this change and made preparations for Leningrad to withstand the expected German assault.