Late Roman military organisation in Britain focused on the threat from the north.
In practice, the military commander, the dux Britannorum dominated Britannia Inferior from Eburacum. From Hadrian's wall to the Humber mouth, the coast was lined with signal stations to communicate along the coast and presumably, warn naval forces of an impending attack.
Forts and naval bases under a comes litoris Saxonici, the Count of the Saxon Shore, defended the coasts of East Anglia, the Thames estuary, Kent and the south coast as far as the Solent. Signal stations have not been found along these coasts. Additional forts and naval forces on the Contentin peninsular, and along the coast of the Pas de Calais up to the Oude Rhijn at Katwijk in Zuid Holland may have been originally controlled by the comes.In late Roman times these resources are listed under the Dukes of Armorica and Belgica Secunda .
The comes Britanniarum commanded a small army of infantry and cavalry in western Britain.
Urban and villa life continued in Maxima Caesarensis and Britannia Prima behind this military shield.
In 407 the usurper Constantine III took the army of Britain to Gaul. There is no evidence for its return after his defeat and death in 411. Without troops, the commands of the Duke and the Counts of Britain could not have been effective.The official connection between Britannia and the Roman empire ended. Although Roman style organisation seems to have persisted until about 450 CE, what governance then remained must be classed as British and Celtic rather than Roman.
There is evidence that Germans were present on the east coast north of the Thames long before the traditional date of the coming of the Saxons. Early Germanic sites near late Roman centres could indicate the settlement of mercenaries. Alemannic and Frisian units are recorded in inscriptions. The reasons for this presence are not known, but Germanic tribesmen and their families could not have been settled in the late Roman landscape except by deliberate Roman policy.
South of the Thames estuary, there is almost no sign of early Germanic presence. The many Romano-British place names preserved in Kent were probably widely known and used by seafaring traders.
Tradition brings the Saxons to Britain around 450.
Traditionally, the Jutes got the island of Thanet in Kent in return for helping Vortigern the local British leader, against the Picts and Scots. When Vortigern lost control, the Jutes left Thanet to ravage and, worse, possess his land.
Sometime later, it seems, Saxons landed in Sussex. They destroyed the, probably British, defenders of the Roman fort at Pevensey (Anderita) and pushed inland.
A larger and even more aggressive band of Saxons landed in Wight and around the Solent. The British were engaged in a bitter war of dispossession and destruction which led to the creation of the kingdom of Wessex and the evacuation of Dumnonia east of the Tamar by the British.
Saxons occupied Essex north of the Thames and initially, most of the east coast. There is early evidence that Saxons were present even in regions that were later to be dominated by Angles.
North of Essex the Anglian groups finally predominated.
Anglian North Folk and the South Folk arrived unrecorded. The Middle Angles settled what became Mercia in silence. Lincolnshire and Yorkshire were lost to the Angles without recording their last days. Roman names are scarce between Lincoln and the Thames.
Comes litoris Saxonici
Count of the Saxon Shore
(ebur "yew" acum "place") York.
(old Rhine) the original Rhine mouth , the "true Rhine".
Duke of Britain
(uer|tigern) a name or title, meaning "Over or high-lord or leader" but not given by Gildas the primary source, who calls the British leader superbus tyrannus
(ande|ritu) great|crossings or fords, the Roman fort at Pevensey
The name Lindum Colonia was preserved almost intact as Lincoln