Saxon Shore Forts of Britannia
During the 3rd century, the Roman Empire was weakened by the succession of brief emperors on the throne, internal fighting and invading tribes encroaching the Empires borders and frontiers.
Britannia was no exception, with repeated Saxon and Frank pirates raiding the coastline. To counteract this Saxon threat, a great chain of forts called the Saxonicum (Saxon Shore) was commissioned to protect the Roman population and strategically important sites from the raiding parties
http://www.heritagedaily.com/2017/10/saxon-shore-forts-britannia/117084
