Before the Holocaust, Lithuania was home to a disputed number of Jews: 210,000 according to one estimate, 250,000 according to another. About 90% or more of the Lithuanian Jews were murdered, one of the highest rates in Europe. The Holocaust in Lithuania can be divided into three stages: mass executions (June–December 1941), a ghetto period (1942 – March 1943), and a final liquidation (April 1943 – July 1944). Unlike in other Nazi-occupied countries where the Holocaust was introduced gradually, Einsatzgruppe A started executions in Lithuania on the first days of the German occupation. The executions were carried out by the Nazis and their Lithuanian collaborators in three main areas: Kaunas (marked by the Ninth Fort), in Vilnius (marked by the Ponary massacre), and in the countryside (sponsored by the Rollkommando Hamann). An estimated 80% of Lithuanian Jews were killed before 1942. The surviving 43,000 Jews were concentrated in the Vilnius Ghetto, Kaunas Ghetto, Šiauliai Ghetto, and Švenčionys Ghetto and forced to work for the benefit of German military industry. In 1943, the ghettos were either liquidated or turned into concentration camps. Only about 2,000–3,000 Lithuanian Jews were liberated from these camps. More survived by withdrawing into the interior of Russia before the war broke out or by escaping the ghettos and joining the Jewish partisans.