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 in winter, when more than 50 per cent of British bird species (over 1500) can be present. Some imported stonework and statuary on the island serves as a habitat for a Mediterranean land snail, "Papillifera bidens". The first records of inhabitants on Brownsea Island occurred in the 9th century, when a small chapel and hermitage were built by monks from Cerne Abbey near Dorchester. The chapel was dedicated to St Andrew and the only resident of the island was a hermit, who may have administered to the spiritual welfare of sailors passing through Poole Harbour. In 1015, Canute led a