From southern East Prussia, XIX Army Corps prepared to advance on Brest-Litovsk (Polish: "Brześć Litewski") with the support of 10th Panzer Division from Army Group North's reserves. They met the bitter resistance of some 700 to 1,000 Polish soldiers under leadership of Władysław Raginis, who managed to slow some 40,000 Germans down for three days at the Battle of Wizna. Multiple lines of bunkers were valiantly defended by the Polish soldiers, and it took the Germans careful maneuvering and a slow advance to eliminate the threat. Guderian refers to this battle as the "Bunkerkampf bei Wizna", 'bunker combat near Wizna'. Raginis, the Polish commander, was killed in action on 10 September 1939 when he committed suicide with a hand grenade after giving his subordinates the order to surrender to the Germans.