On the night of 29–30 August 1706, a party of French grenadiers crept into a large trench, which had been the site of a failed assault on the citadel. The Piemontese had lit bonfires in the trench to burn dead bodies, and this meant that the French grenadiers were not observed. The French grenadiers attacked a small number of Savoyard soldiers at the base of the trench, who were guarding an entrance to the Savoyard mines. The French grenadiers killed them and entered the upper level of the mines.