Yarmouth Castle is a small off-square blockhouse built by Henry VIII in 1547, to guard Yarmouth harbour on the Isle of Wight. It was built as part of Henry's second device programme to fortify the English coast with a chain of coastal defences known as Device Forts or Henrician Castles. These were built to guard against the threat of foreign invasion. As it is a later fortification it did not have the earlier rounded or concentric shape but a square keep with angular bastions. It is now owned by English Heritage.