Southsea Castle was built as a consequence of international tensions between England, France and the Holy Roman Empire in the final years of the reign of King Henry VIII. Traditionally the Crown had left coastal defences to local lords and communities, only taking a modest role in building and maintaining fortifications, and while France and the Empire remained in conflict, maritime raids were common but an actual invasion of England seemed unlikely.; Modest defences based around simple blockhouses and towers existed in the south-west and along the Sussex coast, with a few more impressive works in the north of England, but in general the fortifications were limited in scale.
