In May, 27,000 French troops invaded the Spanish Netherlands and defeated the Spanish at Les Avins, then attacked Leuven on 24 June where they were joined by the Dutch. The besieging army disintegrated due to disease and starvation and withdrew from Leuven after the arrival of a Spanish relief force under Ottavio Piccolomini on 4 July. Led by Cardinal-Infante Ferdinand of Austria, the Spanish took the initiative and captured Limbourg, Gennep, Diest, Goch, then besieged Dutch garrisons in the Duchy of Cleves. The French retreated across the border while the Dutch under Frederick Henry marched urgently on the key strategic position of Schenkenschans. Captured by the Spanish on 28 July, it was recovered only after a long and costly siege.