Lower Dnieper Offensive
The scale of Soviet/German operations during World War II is really mind-boggling. This is an 88 mile front that the Soviets opened up in late September 1943, (the red balloons are Soviet bridgeheads).
Over 4,000,000 men participated in what is called the Lower Dnieper River Offensive. That's like 2x the scale of Stalingrad and this offensive is by no means the biggest battle/offensive conducted during the fighting on the Eastern Front.