The Cautionary Towns were three strategic Dutch towns which, under the 1585 Treaty of Nonsuch, were held by English troops as security for assistance provided by Elizabeth I during the Eighty Years' War against Spain. They included Brill (Brielle) in Holland and Flushing (Vlissingen) and Fort Rammekens on the nearby island of Walcheren. The bases were returned to the Dutch Republic in 1616.