The Battle of Moscow was supposed to be the battle that would end the Eastern Front in World War II, but the German army was stopped by the mud and winter. In fall of 1941, the Wehrmacht was closing in on Moscow and the Soviet forces were desperate. They had lost more than half of their initial strength, and the Germans appeared unbeatable.
Fortunately, the winter set in and greatly slowed down the Germans, who lacked winter clothing and were unprepared for the freezing temperatures. Then, when it became clear that Japan would not invade from Siberia, Stalin was able to redeploy the vast forces he had reserved there and sent them smashing in against the worn down Germans.
The Germans were forced back, despite being so close to Moscow that they could see the Kremlin. Eventually, the Soviet offenses petered out as well and the frontlines stabilized, where they would remain until the Germans would attempt to take Stalingrad in the next year. The Soviets ended up with over 1,000,000 dead and wounded during the battle, while the Germans suffered 171,000 killed.