The smallest front of the war was in Catalonia. In 1689 the Duke of Noailles had led French forces there aimed at bringing further pressure to bear on the Spanish by re-igniting a peasant rising against Charles II, which initially broke out in 1687. Exploiting the situation, Noailles captured Camprodon on 22 May, but a larger Spanish army under the Duke of Villahermosa forced him to withdraw back to Roussillon in August. The Catalan campaign settled down in 1690, but a new front in Piedmont-Savoy proved more eventful. A ferment of religious animosities and Savoyard hatred of the French produced a theatre characterised by massacres and atrocities: constant guerrilla attacks by the armed populace were met by draconian reprisals. In 1690 Saint-Ruth took most of the Victor Amadeus II's exposed Duchy of Savoy, routing the Savoyard army in the process until only the great fortress of Montmélian remained in ducal hands; while to the south in Piedmont, Nicolas Catinat led 12,000 men and soundly defeated Victor Amadeus at the Battle of Staffarda on 18 August. Catinat immediately took Saluzzo, followed by Savigliano, Fossano, and Susa, but lacking sufficient troops, and with sickness rife within his army, Catinat was obliged to withdraw back across the Alps for the winter.
Question: How many fortresses did Nicolas Catinat take after defeating Victor Amadeus at the Battle of Staffarda?
Answer: 4