Construction of Portus Adurni

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The Romans built a massive stone fort on the northern shore of Portsmouth Harbour as part of the Saxon Shore defensive chain. The fort, known as Portus Adurni, enclosed roughly nine acres within walls up to twenty feet high, reinforced with D-shaped bastions. It was designed to defend the harbour against Saxon raids and to serve as a naval base. The walls, built of flint and bonding courses of tile, survive almost to their full height on all four sides, making Portchester the best-preserved Roman fort in northern Europe.