Portchester Castle
With a commanding position over the harbor, this medieval castle is surrounded by what is believed to be the most complete set of Roman walls and the best preserved Roman fort north of the Alps, built in the 3rd century to fend off Saxon pirates. On its completion in the mid-12th century, the castle was appropriated by Henry II and remained a royal residence until the 17th century. From the keep's central tower you can take in sweeping views of the harbor and coastline.
