Polish forces abandoned the regions of Pomerelia (the Polish Corridor), Greater Poland and Polish Upper Silesia in the first week. The Polish plan for border defence was a dismal failure. The German advance, as a whole, was not slowed. On 10 September, the Polish commander-in-chief, Marshal Edward Rydz-Śmigły, ordered a general retreat to the south-east, towards the Romanian Bridgehead. Meanwhile, the Germans were tightening their encirclement of the Polish forces west of the Vistula (in the Łódź area and, still farther west, around Poznań) and penetrating deeply into eastern Poland. Warsaw, which had undergone under heavy aerial bombardment since the first hours of the war, was attacked on 9 September and was put under siege on 13 September. Around then, advanced German forces also reached Lwów, a major city in eastern Poland, and 1,150 German aircraft bombed Warsaw on 24 September.