The Palmiry massacre was a series of mass executions carried out by Nazi German forces, during World War II, near the village of Palmiry in the Kampinos Forest northwest of Warsaw. Between December 1939 and July 1941 more than 1700 Poles and Jews – mostly inmates of Warsaw's Pawiak prison – were executed by the SS (Schutzstaffel) and Ordnungspolizei in a forest glade near Palmiry. The best documented of these massacres took place on 20–21 June 1940, when 358 members of the Polish political, cultural, and social elite were murdered in a single operation. Palmiry is one of the most infamous sites of German crimes in Poland, and "one of the most notorious places of mass executions" in Poland. Along with the Katyn massacre, it has become emblematic of the martyrdom of Polish intelligentsia during World War II. Warsaw was perceived by Nazi leaders as one of the biggest obstacles to their plan to subjugate the Polish nation. After the Nazi invasion of Poland, Warsaw was reduced to a provincial city in the newly created General Government. However, it remained a center of Polish cultural life. Warsaw also headquartered the high command of the Polish Underground State and soon became a stronghold of armed and political resistance against the German occupation. On 14 December 1943 Governor-General Hans Frank noted in his diary: There is a one place in this country which is a source of all our misfortunes – it is Warsaw. Without Warsaw we wouldn't have four-fifths of the troubles which we're facing now. Warsaw is the focus of all disturbances, the place from which discontent is spread through the whole country. The Polish capital surrendered to the Wehrmacht armies on 28 September 1939. Three days later members of Einsatzgruppe IV led by SS-Brigadeführer Lothar Beutel entered the city. They immediately conducted a search in public and private buildings, as well as mass arrests. On 8 October 1939 about 354 Polish teachers and catholic priests were detained because occupational authorities assumed that they are “full of Polish chauvinism” and “created an enormous danger” for public order.