 Complete the following phrase:  The assault started on 6 September 1831. Russian forces surprised the Poles by attacking the strongest Polish position in the suburb of Wola. Despite staunch defence of some of the ramparts, especially Fort 54 and Fort 56, after the first day the outer line of Polish defences had been breached by Russian infantry and artillery. The following day fights resumed, but this time Russian artillery was close enough to shell the western boroughs of the city itself. Although losses were similar on both sides, Polish authorities decided not to risk another 