The battle began in the Seelow Heights, 17 km west of the Oder and 45 km east of Berlin. They were well defended by the "Wehrmacht". On 16 April, the Red Army and the Polish Army attacked Seelow Heights. Almost 1,000,000 attackers, with 20,000 artillery pieces, were fighting against 100,000 Germans with 1,200 tanks, but the German defenders managed to hold the heights for four days.