Fort Knokke or Fort de Cnocke or Fort de la Knocque or Fort de Knocke was an important fortification that defended western Flanders from the 1580s until it was demolished in the 1780s. During its 200 year history, the place was held by the Spanish Empire, Kingdom of France, Habsburg Austria and the Dutch Republic. The existing defenses were improved in 1678 by the famous military engineer Sébastien Le Prestre de Vauban. The fort was attacked by the Grand Alliance in 1695 during the Nine Years' War but the French garrison successfully held out. It was captured from the French by a ruse in 1712 during the War of the Spanish Succession. Control of the fort and other strong places in the Austrian Netherlands was a key feature of the so-called Barrier Treaty in 1713. The French captured the fort after a two-month siege in 1744 during the War of the Austrian Succession. Emperor Joseph II had the citadel demolished in 1781. The site is on the Yser River about 8 kilometres southwest of Diksmuide, Belgium.