Battle of Stalingrad
German and Soviet forces fought for more than five months in the streets of Stalingrad on the Volga. The Soviets encircled and forced the surrender of the German Sixth Army, turning the tide of the war in the east.

Zelma / Георгий Зельма · CC BY-SA 3.0 · Source
In summer 1942 the Germans drove south towards the Caucasus oil fields and attacked Stalingrad. Bombing reduced the city to ruins, and the fighting went on building by building and factory by factory.
On 19 November Soviet forces broke through the weak Romanian lines on either side of the city and encircled some 300,000 men of the German Sixth Army (Operation Uranus). Hitler forbade a breakout; the trapped army starved and froze, and on 2 February 1943 its last 90,000 or so surrendered. Casualties on both sides are estimated at close to two million, making it one of the bloodiest battles in history.