On 18 May, Souham determined to hurl 40,000 men at the Duke of York's three columns, while holding Kinsky, Charles and Clerfayt off with secondary forces. During the night, Clerfayt managed to cross to the south bank of the Lys. His 21,000 men drove back Vandamme's 12,000, but he was unable to advance south beyond Linselles. Shaken by his defeat the day before, Bussche retreated to the Scheldt River. In the south, Charles and Kinsky remained almost completely inert, despite Mack's frantic orders for them to march to Lannoy. Instead, Charles became obsessed with protecting his left flank and rear from French incursions.