WEIMAR, Germany (AP) _ Army Lt. Col. Jim Moncrief received an urgent radio message about piles of bodies at a nearby concentration camp. He jumped in a jeep and headed for the place, ringed by barbed wire and watchtowers, atop Ettersberg Hill.

The Nazis called it Buchenwald.

``I saw fully dressed bodies lying around. I thought they were taking a nap in the sun. But indeed they were dead,'' recalls Moncrief.

Some of those who were still alive, starved and diseased, moved like zombies around the rows upon rows of filthy barracks.

Moncrief, a division staff officer with Gen. George Patton's Third U.S. Army, went inside one of the barracks.

``Bony survivors were lying on stacked bunks. Some of them didn't even have enough life to turn their heads to see the stranger coming in,'' Moncrief, now 83 and a retired colonel, said in a telephone interview from his home in Monroe, N.C.

Buchenwald, named after the surrounding beech forest, was the first large concentration camp encountered by American troops during World War II.

Its survivors and the veterans who rescued them will come together this weekend for ceremonies marking the 50th anniversary of liberation.

From the first prisoners' arrival in 1937 to the camp's liberation, at least 56,000 people died at Buchenwald.

The GIs found piles of bodies, three mass graves and 21,000 inmates _ among them Russian and Polish POWs, Jews and Gypsies _ who had managed to avoid death.

The world already knew of Auschwitz, liberated by the Soviets nearly three months earlier. But reports from there were so horrific that many people at first did not want to believe they were true.

It became clear at Buchenwald that atrocities had been committed all across the Third Reich. Before the Nazis' surrender on May 8, 1945, about 11 million people died in some 520 concentration camps. The largest group of camp victims were Jews.

Buchenwald survivors told of the SS murdering inmates by injecting poisons into their hearts, drowning prisoners in open latrines and working them to death at the nearby stone quarry.

Natan Zim, a Polish Jew, and his older brother, Jacob, were among the prisoners who survived to witness the Americans' arrival.

Natan was 15 at the time.

Prisoners' hopes had been raised in early April 1945 by the distant sound of artillery as Patton's Third U.S. Army approached from the west.

In the first two weeks of April, more than 20,000 prisoners were forced out of the camp by train and on foot to keep them from being rescued.

The Zim brothers _ who had already been evacuated from Auschwitz, where they lost their parents _ avoided the forced march out of Buchenwald by hiding in a crawlspace beneath their barracks.

``We were in that hole for two days. I had one thought: I wanted to be free,'' Natan Zim said in a telephone interview from his home in Tel Aviv, Israel, before heading to Germany for the reunion.

At about 2 p.m. on April 11, American tanks appeared in the forest. There was gunfire. Most of Buchenwald's 5,000 SS guards had already fled.

Prisoners picked up weapons dropped by guards and captured the 76 Nazis who remained. A white flag was raised above the camp command tower.

The Army patrol team entered Buchenwald, then Moncrief, and then more GIs in jeeps.

The Zim brothers came out of hiding.

``The Americans gave me chocolate and chewing gum,'' Zim remembers. For a boy who had wasted away to skin and bones from two brutal years in Nazi camps, it was a feast.

Patton was so disgusted by Buchenwald that he ordered 1,000 residents of nearby Weimar to march four miles up Ettersberg Hill to see what had been going on in their neighborhood.

The Weimar citizens were forced to look at hooks where prisoners had been hanged, and at body parts and bones in the camp crematorium.

Gen. Dwight D. Eisenhower invited American war correspondents to Buchenwald, and war correspondent Edward R. Murrow told his American radio audience about Nazi atrocities in a famous April 15, 1945, broadcast.

``I pray you to believe what I have said about Buchenwald,'' Murrow said. ``I have reported what I saw and heard, but only part of it. For most of it I have no words.''