After the German invasion of Poland in September 1939, the proximity of the border once again proved disastrous. Kalisz was captured by the Wehrmacht after Polish resistance, and the city was annexed by Germany. In revenge for resistance, the Wehrmacht carried out massacres of Polish defenders, who were executed both in the city and in the nearby settlement of Winiary (today a district of Kalisz). Over 1,000 people were arrested as hostages. Numerous Poles were arrested and murdered during the "Intelligenzaktion" aimed at annihilation of the Polish intelligentsia. Around 750 Poles from Kalisz, Ostrów Wielkopolski and other nearby settlements were imprisoned in the Kalisz prison from September 1939 to March 1940, and most were murdered in large massacres in the Winiary forest. In November 1939, the "Einsatzgruppe VI" murdered 41 Poles at the local Jewish cemetery, among the victims was pre-war Polish mayor of Kalisz, Ignacy Bujnicki. In April and May 1940, many Poles arrested in the region, especially teachers, were imprisoned in the local prison, and afterwards deported to the Mauthausen and Dachau concentration camps, where they were murdered.