The Roman occupation of Britain was at its end, Roman ways such as coinage and civilisation were also over. Over time these ways were replaced with the ways and traditions of the oversea invaders, the Anglo-Saxons. Their culture and then their language became Britains way of life.
The Anglo Saxons were not as orgainised as the Romans colonising slowley northwards and westwards, forcing the native Celts to the fringes of Britain. These included Cornwall, Wales and Scotland. With the Celtic people at the furthest reaches of Britain's relams, Roman Britain was replaced by Anglo Saxon Britain.
By 850 AD the Anglo Saxon colones eventually combined into 3 kingdoms; Mercia, Northumbria and Wessex.
However Hertfordshire is still one of the southen counties to produce significant evidence of Anglo-Saxon settlements.