The revolution in Vienna sparked anti-Habsburg riots in Milan and Venice. Field Marshal Joseph Radetzky was unable to defeat the Venetian and Milanese insurgents in Lombardy-Venetia, and had to order his forces to evacuate western Italy, pulling his forces back to a chain of defensive fortresses between Milan and Venice known as the Quadrilatero. With Vienna itself in the middle of an uprising against the Habsburg Monarchy, the Austrian Empire appeared on the brink of collapse. On 23 March 1848, just one day after Radetzky was forced to retreat from Milan, The Kingdom of Sardinia declared war on the Austrian Empire, sparking the First Italian War of Independence.