In the second relief of Mantua, Wurmser and his chief-of-staff Franz von Lauer planned to transfer major elements of the army from the upper Adige valley to Bassano del Grappa via the Brenta valley. They assigned Davidovich to hold the Adige valley with 13,500 soldiers in the brigades of the Prince of Reuss, Josef Vukassovich, and Johann Sporck. Lauer believed that the French army would remain passive during the operation. Defying expectations, Bonaparte attacked Davidovich with 30,000 men. In the Battle of Rovereto on 4 September, the French swamped the Austrian defenses, inflicted 3,000 casualties, captured Trento, and pushed Davidovich north beyond Lavis. Bonaparte soon won the Battle of Bassano and drove Wurmser and 12,000 men within the fortress of Mantua.