The Saxon Shore or litus Saxonicum (1) was a defensive system comprising a series of shore forts built by the Romans, mostly in the late third century AD, to defend the south east coast of Britannia against the threat of piratical raids.
We know of the existence of this defensive system due to the Notitia Dignitatum a later, fifth century collection of documents that lists the military establishment of the Roman Empire. According to the Notitia Dignitatum there were a total of nine forts under the command of the Comes litoris Saxonici per Britannias, the Count of the Saxon Shore (3), listed as follows;
At Walton Castle
in Old Felixstowe
there was (2)
another Roman fort, which is sometimes included as part of the Saxon Shore, but it was not listed as such in the Notatia.
Most were built between 276 and 285, although the forts at Brancaster and Reculver already existed as bases for the Classis Britannica, the Roman fleet in Britain, and the fort at Pevensey was a later addition. They probably operated in conjunction with similar forts on the Gallic coast as well as the fleet.
As it is only the Notitia Dignitatum that mentions the existence of the Saxon Shore system it is unclear as from what date this system of forts was called the Saxon Shore. Opinions also differ as to why it was called the Saxon shore; some argue that because it was the shore attacked by Saxons, others because it was settled by Saxons. The later is unlikely as the listed garrisons from the Notatia are all regular troops with no Saxon links.
(1) My thanks go to Gritchka for assistance in getting the Latin right here.
(2) Was, because the sea has washed away the site on which it stood.
(3) The actual office of the Count didn't come into existence until later in the fourth century as it was the emperor Constantine who inaugurated the imperial rank of comes.