In March 1848, the city of Milan launched an uprising against Austrian occupation. Charles Albert supported the Milanese revolt and declared war on Austria. Venice also declared its independence from Austria. The Austrian Field Marshal Radetzky withdrew his forces from Milan to the defensive positions based on the four fortresses known as the "Quadrilateral": Verona, Mantua, Peschiera, and Legnago. The Piedmontese took Peschiera after a short siege, but Radetzky received substantial reinforcements.