FACTBOX: Key facts on main Nazi camps

(Reuters) - The trial of John Demjanjuk started on Monday on charges that as a Nazi guard he helped to force 27,900 Jews into gas chambers at Sobibor death camp in 1943.

The 89-year-old denies involvement in the Holocaust.

Here are some details about the main Nazi camps:

AUSCHWITZ:

-- German forces occupying Poland set up Auschwitz in southern Poland in 1940 as a labor camp for Polish prisoners, gradually expanding it into a vast labor and death camp.

-- The complex contained three camps and at least 36 sub-camps which were built outside the town of Oswiecim, on an isolated 40 sq km (15 sq mile) site, between 1940 and 1942.

-- Auschwitz I was built for Polish political prisoners in June 1940. Above its entrance gate is written the motto “Arbeit macht frei” (Work makes you free).

-- Auschwitz II was built in October 1941 in Birkenau, 3 km from the main camp. It held more than 100,000 and was the main site of mass killings. Gas chambers and crematoria capable of disposing of about 2,000 people a day were built there. By 1944, 6,000 a day were being killed.

-- Auschwitz III supplied forced labor for the nearby I.G. Farben chemical plant. Between 1.2 and 1.5 million people died at the camps, most of them Jews.

-- Other groups of victims included Polish political prisoners, Soviet prisoners of war, Gypsies, homosexuals, people with disabilities and prisoners of conscience or religious faith. The camp was liberated by Soviet forces on January 27, 1945.

* SOBIBOR:

-- Built in March 1942, Sobibor operated from May 1942 until October 1943. It was built near the village of Sobibor near Chelm in Poland.

-- Sobibor’s gas chambers killed at least 250,000 Jews. Most came from Poland and from the occupied areas of the Soviet Union and Western Europe.

-- Sobibor was the scene of the war’s biggest prisoner escape. On October 14, 1943, about 600 prisoners escaped, killing several SS supervisors and Ukrainian guards. Several inmates were killed during the rebellion or during the escape attempt. All who stayed behind were executed the next day.

* BUCHENWALD:

-- Set up in 1937 to house political detainees, the camp was one of the largest, with 130 satellite camps and extension units. It was situated on the northern slope of Ettersberg, in eastern Germany. The first 149 prisoners arrived on July 15, 1937. At that time, the camp was called Ettersberg but later changed to Buchenwald.

* Between July 1937 and April 1945, 250,000 people from around Europe were imprisoned in the camp. The number killed is estimated at 56,000. Of these, 34,375 were registered in the camp records. From the beginning of 1945 and its liberation, 13,969 people died at Buchenwald.

* DACHAU:

-- In March 1933, a concentration camp for political prisoners was set up in Dachau near Munich.

-- In the 12 years of its existence over 225,000 persons from all over Europe were imprisoned there and in the numerous subsidiary camps. At least 41,000 were killed. On April 29, 1945, American troops liberated the survivors.

* BERGEN-BELSEN:

-- Bergen-Belsen was situated near Hanover and was officially a sick camp which imprisoned soldiers and Soviet prisoners of war. Up to early 1942 approximately 18,000 captives died of hunger, cold and disease.

-- By March 1945 its numbers had grown to about 60,000. Anne Frank was imprisoned and died there. When the British liberated it, they found 10,000 unburied dead and mass graves containing around 40,000 bodies. Of the nearly 40,000 still alive, many thousands died soon after.

* MAUTHAUSEN:

-- The main camp was opened near Linz in August 1938, just weeks after the Nazi occupation of Austria. It housed Jews from Europe. About 206,000 people were imprisoned there, of whom over 70,000 were killed from overwork in stone quarries and armament industries as well as starvation and illness. The camp was liberated on May 5, 1945