In August, Jourdan crossed and quickly seized Düsseldorf. The Army of the Sambre and Meuse advanced south to the Main River, isolating Mainz. On 20 September 1795, 30,000 French troops under the command of Jourdan laid siege to Mainz. The Coalition garrison of 9,600 negotiated secretly with the French to relinquish the fortress. The French subsequently used the city as a staging area for much of the 1795 campaign.