The Siege of Leuven (June 24 – July 4, 1635) was an important siege in the Thirty Years' War in which a Franco-Dutch army under Frederick Henry of Orange and the French Marshals Urbain de Maillé-Brezé and Gaspard III de Coligny, who had invaded the Spanish Netherlands from two sides, laid siege to the Spanish city of Leuven, defended by 4,000 Flemish civilians, Walloons, Spaniards and Irish under Anthonie Schetz, Baron of Grobbendonck.