Decline of Romano-British Kent
Roman fort wall at Regulbium
In the Romano-British period, the area of modern Kent that lay east of the River Medway was a civitas known as Cantiaca. Its name had been taken from an older Common Brittonic place-name, Cantium ("corner of land" or "land on the edge") used in the preceding pre-Roman Iron Age, although the extent of this tribal area is unknown.
During the late third and fourth centuries, Roman Britain had been raided repeatedly by Franks, Saxons, Picts, and Scots. As the closest part of Britain to mainland Europe, it is likely that Kent would have experienced many attacks from seafaring raiders, resulting in the construction of four Saxon Shore Forts along the Kentish coast: Regulbium, Rutupiae, Dubris, and Portus Lemanis. It is also likely that Germanic-speaking mercenaries from northern Gaul, known as foederati, would have been hired to supplement official Roman troops during this period, with land in Kent as payment. These foederati would have assimilated into Romano-British culture, making it difficult to distinguish them archaeologically.
There is evidence that over the fourth and early fifth centuries, rural villas were abandoned, suggesting that the Romano-British elite were moving to the comparative safety of fortified urban centres. However, urban centres also witnessed decline; Canterbury evidenced a declining population and reduced activity from the late third century onward, while Dover was abandoned by the end of the fourth century.
In 407, the Roman legions left Britain in order to deal with incursions into the Empire's continental heartlands. In 410, the Roman Emperor Honorius sent a letter to his British subjects announcing that they must thenceforth look after their own defence and could no longer rely on the imperial military to protect them.
According to the Anglo-Saxon Chronicle, produced in late Anglo-Saxon England and not considered an accurate record of events in the fifth century, in 418 many Romans left Britain via Kent, taking much of their wealth with them. This may represent a memory of a genuine exodus of the Roman aristocracy.