to the defenders of Warsaw. Siege of Warsaw On 15 September, the German Third Army from Army Group North attacked Praga. They attacked from both sides of the Vistula. After heavy fighting for the Grochów area the German 23rd Infantry Regiment was annihilated by the Polish defenders of the 21st "Children of Warsaw" Infantry Regiment under colonel (later promoted to general) Stanisław Sosabowski. After the Battle of Bzura ended, the remnants of the Poznań Army and the Pomorze Army broke through the German encirclement and arrived in Warsaw and Modlin between 18–21 September from the Kampinos Forest. After that the forces of the defenders amounted to approximately 140,000 soldiers. The German forces preparing for an all-out assault numbered 13 divisions with one thousand artillery pieces. On September 22 the last lines of communication between Warsaw and Modlin were cut by German forces reaching the Vistula. As preparation for the storming, the city was shelled day and night with artillery and aerial bombardment. Among the guns used were heavy railway guns and mortars. Two entire air fleets took part in the air raids against both civilian and military targets. After September 20 the forces on the eastern bank of the Vistula started daily attacks on the Praga suburb. All were successfully counter-attacked by the Polish forces. On September 24 all German units concentrated around Warsaw were put under command of general Johannes Blaskowitz An initial German attack took place on 23 September, which was successfully repulsed. On September 25 the next attack started with an artillery and air bombardment, including 1,200 aircraft. This so-called "Black Monday" became a legend in the history of Warsaw. The following day in the early morning the general assault was started on all fronts of surrounded Warsaw. Western parts of the city were attacked by 5 German divisions (10th, 18th, 19th, 31st and 46th) while the eastern part was attacked by 4 divisions (11th, 32nd, 61st and 217th). The attack was supported by approximately 70 batteries of field artillery, 80 batteries of heavy artillery and two entire air fleets (1st and 4th), which bombarded the city continuously causing heavy losses in the civilian population. On 26 September, the Forts of Mokotów, Dąbrowski and Czerniaków fell to the German assault. Capitulation and surrender General Czuma managed to gather enough forces and war material to successfully defend the city for several weeks longer. However, the situation of the