aerial photograph of Portus Lemanis - Lympne Roman Fort and Port in Kent England UK. Portus Lemanis was founded around the 2nd century AD and was used continually until the Romans withdrew from Briatin in the fifth century. The port continued to be used for some time after that but disappeared from the historical record after the seventh century. The fort, also known as Stutfall Castle , was constructed around 270AD and one of the Saxon shore forts intended to defend against Saxon raiders . At one point the fort was garrisoned by a cohort of troops from Belgium. Today the sea has receded and the unstable clay soil has caused the remains to move and crumble..