General Rómmel advanced with a small contingent of forces through towards Warsaw, where he assumed command of the improvised Warsaw Army tasked with defending the Polish capital (see siege of Warsaw), but he left most of his forces behind. General Wiktor Thommée assumed command of the remaining units. Piotrków Group, or as it became known after its commander, Thommée's Group, was much more successful, managing to avoid encirclement, and after the Battle of Wola Cyrusowa (September 8) his corps' last battle was the defence of the Modlin fortress (capitulated on 29 September).