The siege of Lille took place during the War of Devolution. Louis XIV's forces besieged Lille from 10 August to 26 September 1667. It was the only major engagement of the war. Lille was the first major victory for Vauban’s siege techniques. Louis XIV, arguing that the Spanish dowry of his wife Maria Theresa of Spain had not been paid, began to expand French borders to the north and east, invading the Spanish Netherlands. This began a conflict with Spain that became the War of Devolution. After taking Charleroi, Tournai and Douai, French troops laid siege to Lille, at that time part of the county of Flanders under Spanish rule. Siege techniques applied by the French military engineer Vauban were instrumental in their capture.