Portland Castle is one of King Henry VIII's chain of coastal artillery forts positioned along the south coast of England. It was built to a unique fan design between 1539-41, using local Portland stone. Together with Sandsfoot Castle, it defended the natural anchorage known as Portland Roads. 

A renewed threat of Spanish invasion lead to the neglected castle being repaired and upgraded with two new gun platforms for the lower and upper keeps between 1584-86. The castle finally saw military action during the mid-1600s, playing a part in the English Civil War and Anglo Dutch War. Over subsequent centuries, it served as either a residence or reverted to military purposes depending on whether the country was at war. Today, it is open to the public and managed by English Heritage.