German chancellor Willy Brandt kneels down in front of a memorial in the former Jewish ghetto in Warsaw, 7 December 1970. The monument is dedicated to the murdered heroes of the rebellion of April 1943. Brandt's kneeling captured the hearts of Polish intellectuals and was the start of reconciliation between Germany and Poland. The same day Brandt signed the Warsaw Treaty which affirms the inviolability of the existing borders (Oder-Neisse-Line) and was a cornerstone agreement in Brandt's 'Ostpolitik' to improve relations with Germany's Eastern neighbours. Germany and Poland agreed to refrain from use of force and to develop and nurture friendly relations. During World War II six million Polish were killed by Germans, more than half of them Jewish.