Roman fort built at Portchester

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The Roman fort at Portchester, known as Portus Adurni, was constructed around 280 AD as one of the chain of Saxon Shore forts built to defend the south coast of Roman Britain from seaborne raiders. The fort was built on a low promontory on the northern shore of what is now Portsmouth Harbour, commanding views across the harbour entrance and the Solent. The fort is rectangular, enclosing an area of about nine acres, with massive flint and stone walls standing up to six metres high and reinforced by twenty D-shaped bastions. The walls and bastions survive to a remarkable degree, making Portchester the most complete Roman fort in northern Europe. The fort was garrisoned throughout the later Roman period and continued in use as a defended site after the Roman withdrawal. Portchester's strategic position at the harbour mouth ensured that it remained important for centuries after the Romans. Saxon settlers occupied the site, a Norman castle was built within the walls, and the fort's outline still defines the layout of the monument that visitors see today.