Brownsea Castle the castle also has four cannons, probably dating from the 17th or early 18th century. The castle is protected under UK law as a Grade II listed building. Brownsea Castle Brownsea Castle, also known historically as Branksea Castle, was originally a Device Fort constructed by Henry VIII between 1545 and 1547 to protect Poole Harbour in Dorset, England, from the threat of French attack. Located on Brownsea Island, it comprised a stone blockhouse with a hexagonal gun platform. It was garrisoned by the local town with six soldiers and armed with eight artillery pieces. The castle remained in use after
Brownsea Island Viking raid to the harbour and used Brownsea as a base to sack Wareham and Cerne Abbey. In the 11th century the owner of the island was Bruno, who was Lord of the Manor of Studland. Following his invasion of England, William the Conqueror gave Studland, which included Brownsea, to his half-brother, Robert de Mortain. In 1154, King Henry II granted the Abbot of Cerne the right of wreck for the island and the abbey continued to control the interests of Brownsea for the following 350 years. After the Dissolution of the Monasteries, control of Brownsea passed to the Crown.