sentences:  Portus Adurni which later became known as Portchester Castle, was one of the Saxon Shore forts and was a major base of the Classis Britannica and possibly its Headquarters.Although there have been settlements in the area since before Roman times, mostly being offshoots of Portchester, Portsmouth is commonly regarded as having been founded in 1180 by John of Gisors (Jean de Gisors).Most early records of Portsmouth are thought to have been destroyed by Norman invaders following the Norman Conquest.