The Cautionary Towns, were three towns in the Dutch Republic garrisoned by English troops from 1585. They were so named because they were given to Queen Elizabeth I as security for the Dutch rebels repaying her for assistance in their struggle with Spain. The towns were Brielle (Briel), Vlissingen (Flushing) and Fort Rammekens on the island of Walcharen.
English and Scots troops who had volunteered to fight for the Dutch Protestant cause had helped to capture Brielle, Rammekens and Flushing in 1572 and garrisoned them soon after. This continued until 1585 with the outbreak of war with Spain. The handover of the garrisons was made during the Treaty of Nonsuch in 1585 and were kept during the Anglo-Spanish war which England would garrison at its own expense. The primary objective was to keep these ports out of Spanish hands.
Robert Sidney, 1st Earl of Leicester was made governor of Flushing in 1588. The first English governor of Brielle was Thomas Cecil, 1st Earl of Exeter, succeeded by Edward Conway, 1st Viscount Conway who named his daughter Brilliana in honour of the city.
When peace was made at the Treaty of London in 1604 the Spanish demanded the return of the Cautionary Towns but the English refused to hand them over. Instead King Philip III of Spain gave in to English refusal which allowed him instead to gain access through the English Channel and Spain viewed the towns as neutral.
The towns were eventually restored to Holland by purchase through King James I in 1616 for the sum of £250,000.