After driving the Austrian army out of northwest and north-central Italy, the French invested the fortress of Mantua starting in early June 1796. In late July, a new Austrian commander, Dagobert Sigmund von Wurmser led an army to the relief of Josef Franz Canto d'Irles' garrison from the north. Mantua was reached and the French were forced to abandon the siege. However, the Austrians were subsequently beaten in the battles of Lonato and Castiglione. Forced to retreat, Wurmser resupplied and reinforced the fortress with food and able-bodied troops. After withdrawing north up the Adige River, Wurmser planned to move his main army through the mountains to Bassano via the Brenta valley. From there he would mount the second relief of Mantua from the northeast. In an exceedingly bold maneuver, Bonaparte smashed Paul Davidovich's covering force and followed Wurmser down the Brenta valley. Overcoming the Austrian army at Bassano in early September, Bonaparte tried to destroy Wurmser but failed. Instead he chased the bulk of the Austrian army into Mantua. The garrison now counted 30,000 men, but cut off from outside help, disease and starvation began mowing down Wurmser's troops.