The Germans created KL Warschau in July 1943, two months after they had crushed the Warsaw Ghetto Uprising and reduced the ghetto's buildings to a vast field of rubble. The camp's first purpose was that rubble — somebody had to clear it. The Germans assigned the work to Jewish prisoners brought from Auschwitz and other camps, including Greek Jews from Salonika and Hungarian Jews deported in 1944. They lived in the ruins of what had been their nation's largest Jewish quarter, sleeping in barracks built by Polish POWs from 1939, eating starvation rations, and taking apart the bricks that had once made up tenements where 400,000 of their fellow Jews had lived and died. Many of them did not survive the work. The camp also held Polish political prisoners, transferred from Pawiak prison nearby, who were often executed in the rubble field. By 1944, KL Warschau had become a satellite of the Majdanek camp system.

When the Warsaw Uprising broke out on 1 August 1944, the Home Army made the rescue of Gęsiówka a tactical priority. The camp held hundreds of foreign Jews — Greek, French, Hungarian, Belgian, Czech — who had survived the original ghetto liquidation only because they had been brought in to clear its ruins. On 5 August, Captain Wacław Micuta led the Zośka battalion in an assault on the camp's gates. They captured a German Panther tank, used it against the camp's defenders, and broke through. The 348 liberated prisoners were hungry, sick, and terrified — and many of them immediately volunteered to fight. They fought as the Jewish Combat Battalion within Zośka and other Home Army units. Most died in the next two months as the uprising was crushed. A handful survived to tell the story. The Gęsiówka liberation remains one of the only documented cases of Polish underground forces freeing Jews from a German camp during the war.

In the late 1970s, a Polish judge named Maria Trzcińska began promoting a different version of KL Warschau's history. She claimed the camp had been a hidden extermination center where the Germans had murdered 200,000 Poles in gas chambers near the Warszawa Zachodnia railway station. There was no evidence for any of it. The barracks she pointed to had been built in the 1930s and had remained accessible to civilians throughout the war. The death wall she identified had been added in 1972. Aerial photography expert Zygmunt Walkowski showed conclusively that no such gas chambers existed. Mainstream historians — Bogusław Kopka chief among them — argue that Trzcińska conflated the actual ghetto deaths, the uprising deaths, and the smaller real death toll of KL Warschau into a single inflated number. Yet plaques citing her figure of 200,000 dead were unveiled in Warsaw in 2017 and at the Jasna Góra Monastery, supported by right-wing media and church authorities. Walkowski, who debunked the gas chamber theory, said he received threats.

The actual death toll at KL Warschau will never be precisely known — perhaps 20,000, perhaps fewer. Many were Polish political prisoners; many more were Jewish forced laborers worked to death in the ruins. The official commemorative site — the plaque liberating Battalion Zośka helped create — sits at the corner of Anielewicza and Okopowa streets, near the camp's southwest corner, written in Polish, Hebrew, and English. A second plaque was unveiled near the Pawiak Prison Museum in November 2013. The 1995 German postage stamp commemorating the liberation of the camps included KL Warschau on its list. In 2020 the National Bank of Poland issued a 10 PLN silver coin honoring the camp's victims. The conspiracy theorists and the historians continue to argue. The 348 liberated prisoners, the unknown Jewish dead, and the Polish underground fighters who freed them deserve more attention than the dispute about how many to inflate the numbers to.