“They were all hit in the back,” said 90-year-old Alexei Stefanov. “But they did not flee.”

Stefanov is among the few surviving veterans of the battle, which claimed 2 million lives and raged for nearly 200 days before the Red Army turned back the Nazi forces, decisively changing the course of the war. Russia celebrates the 70th anniversary of that victory on Saturday, with President Vladimir Putin taking part in ceremonies in Volgograd, the current name of the city in southern Russia that stretches along the western bank of the Volga River.

Stefanov arrived in Stalingrad in August, 1942, just a month after the Nazis began their onslaught. A marine, he commanded what was left of a reconnaissance platoon, 17 scouts who had survived previous missions on the front lines.

The German army invaded the Soviet Union in June, 1941, and by the following summer had pushed deep inside the country. For Adolf Hitler, taking the city named after Soviet dictator Josef Stalin would be a symbolic victory, and it also would allow the Germans to cross the Volga and secure access to Russian oil supplies.

What Stefanov saw was a once-thriving industrial city being reduced to rubble by shelling and bombing by the Nazis and their Romanian, Italian, Hungarian and Spanish allies. Only about 100,000 residents had been evacuated, and the remaining civilians were frantically helping to dig trenches.

The Red Army had orders from Stalin not to retreat, so only women, children and wounded soldiers were allowed to take the crossing over the wide river to relative safety.

The day Stefanov remembers most vividly is Aug. 23, 1942, when hundreds of Nazi planes bombed the city, turning it into a giant burning ruin. Hundreds of Soviet soldiers with wounds bad enough to keep them out of the battle but not severe enough to incapacitate them set out to rescue women and children from the basements of demolished buildings. They rushed them to ferries that would take them across the Volga, a river about 2 kilometers (more than 1 mile) from shore to shore.

Fires from spilled oil and gasoline burned on the water, and the defenseless ferries were easy prey for the Nazi planes. The Soviet soldiers covered the children with their own bodies. Stefanov is still haunted by the sight of the soldiers who died, their backs ripped apart.

In the city, thousands of dead bodies were left unburied, lying amid the ruins in the sweltering August heat. For the only time during the Battle of Stalingrad, German tanks got to the river, and Soviet tanks and artillery fiercely fought them back.

“That was hell, literal hell,” Stefanov said. “This one episode to me was equal to the whole war.”

Stefanov recalls reconnaissance missions deep inside enemy territory, when he had to crawl for hours and hide in ravines to gather intelligence on the location and number of Nazi troops and weapons.

In September, 1942, Stefanov was hit in his left hand, a wound that still troubles him. He later returned to active service and was with Soviet troops when they drove the Germans out of Norway and marched into Warsaw and Berlin.

He was back in Moscow in late June, 1945, to participate in the Victory Parade on Red Square. Then he went on to China to help drive out the imperial Japanese.

Stefanov’s contribution to the war effort won him dozens of medals. Although they weigh a combined 11 kilograms (24 pounds), he still wears them pinned to the front of his uniform on holidays and other special occasions.

His real reward at the end of the war was his marriage to Lyudmilla, also a decorated war veteran. They are still together 67 years later.

“War is not a game, it’s the most horrible thing,” said Stefanov, who heads a government-run organization of World War II veterans. “That’s the thing youngsters should always know.”