The allies were still in occupation of the three fortresses--Valenciennes, Condé, and Le Quesnoi--which they had taken in the preceding year. Between Valenciennes and Bavay was the Austrian centre; their right wing occupied Flanders, their left guarded the line of the Sambre. Carnot’s plan was to make use of his numerical superiority, first to shatter the enemy’s wings, and then, attacking his centre both in front and in flank, to drive him out of Belgium. The Austrians began hostilities by laying siege to Landrecies. Pichegru, with 100,000 men, advanced into Flanders, and defeated the allied right wing at Turcoing (April 18). He next laid siege to Ypres, and the allies, after an ineffectual attempt to relieve the town, retreated behind the Scheldt. On the Sambre the allied forces were equal in number to the French, both armies being about 50,000 strong; and here, while Pichegru was conquering Flanders, an effectual stand was made against the repeated efforts of the French generals to get a footing on the north side of the river and to invest Charleroi. But the continued inactivity of the Prussians enabled Carnot to send 50,000 men from the Rhine to the Sambre, so as to outnumber the allies on this side also. Charleroi was invested, and capitulated (June 25). The following day Coburg, who had arrived from the centre with reinforcements and was unaware of the surrender, attacked the French positions at Fleurus and the neighbouring villages (June 26). The battle lasted the whole day, without decided result; and Coburg, on hearing that Charleroi had already surrendered, did not renew the struggle. The evacuation of Belgium followed these disasters. Coburg withdrew behind the Meuse, and the Duke of York, with the English and Dutch troops, retreated into Brabant. The French laid siege to those fortresses in France and Flanders in which the allies had left garrisons.