When the revolution of 1848 broke out, Cattaneo became one of the leaders of the insurrection against the Austrians, known as the Five Days of Milan (18–22 March 1848). Together with the young democrats Enrico Cernuschi, Giulio Terzaghi and Giorgio Clerici he formed a council of war which, having its headquarters at Palazzo Taverna in via Bigli, directed the operations of the insurgents. When on March 18 Field Marshal Radetzky, feeling that the position of the Austrian garrison was untenable, sounded the rebels as to their terms, some of the leaders were inclined to agree to an armistice which would give time for the Piedmontese troops to arrive (Piedmont had just declared war), but Cattaneo insisted on the complete evacuation of Lombardy. Again, on 21 March, Radetzky tried to obtain an armistice, and Durini and Borromeo were ready to grant it, for it would have enabled them to reorganize the defences and replenish the supplies of food and ammunition, which could only last another day. However, Cattaneo replied: