sentences:  On 8 September General Juliusz Rómmel, the commander of the Łódź Army who had become separated from his operational units, arrived in Warsaw with his staff.The chief of staff of the Polish Armed Forces, general Wacław Stachiewicz (then in Brześć), appointed him the overall commander of all forces defending Warsaw, including the Warsaw Defense Force, the Modlin Fortress and the army units immediately south and north-east of Warsaw 
  
  During the next days, army units retreating in face of the onslaughts of the German armor and under continuous air attacks, fought their way through the German lines to the besieged capital, in particular from the Battle of Bzura.After 13 September Warsaw and Modlin were effectively surrounded.