Wurmser's force of 33,599 infantry and 9,635 cavalries had whittled away at the Lines, skirmishing throughout August and September with French infantry and cavalry, which always withdrew to the superior defensive position behind the earthen works. While the Prussians marched around the lines, from Pirmasens, Wurmser organized his force into seven columns, and they assaulted the Lines in waves. In the First Battle of Wissembourg on 13 September the French defenses were successfully breached.