Although an integral part of the Empire, Britannia required a large Roman garrison throughout its centuries under Roman control, firstly to deter attacks from the tribes north of Hadrian’s Wall. As Imperial might waned, barbarian raiders became bolder. The south and east coast were lined with forts to protect against sea-borne raiders, its commander bearing the title of Count of the Saxon Shore for Britain (comes littoris Saxonici per Britanniam), one of three military governors of Britannia, the other two ruling the central and northern regions of the diocese.

Having under command powerful legions stationed far from Rome, the men tasked with guarding Rome’s border had a powerful temptation to get involved in the power struggles that wracked the Empire at the end of the fourth century. Magnus Maximus stripped Britannia of its troops when he made a bid for the purple in 383. His rebellion began in north Wales and for a time he ruled half the Empire: Britannia, Gaul, Spain and Africa. According to later Welsh traditions, Magnus handed power over to local rulers when he left the country and early Welsh genealogies list Magnus as the founder of later Welsh kingdoms, including Gwent and Powys.

After the last attempted usurper, Constantine III, left Britannia in 407, effective Roman rule in the diocese came to an end. But it was not an abrupt end. While political power had drained away from the Empire, many of the inhabitants of Britannia still thought of themselves as Roman and they continued to live, as far as was possible, as Romans should. While urban life declined, the Romano/British elite built themselves rural villas within which a version of Roman life continued in many places well into the 5^th century. Although some cities were abandoned, Carlisle, Wroxeter, Winchester and Gloucester continued as functioning towns throughout the 5^th century and even into the 6^th century. However, Roman coinage pretty well ceased coming into the country after the first decade of the 5^th century. Without fresh coinage arriving, it probably took twenty or thirty years for the money-based economy to collapse. At roughly the same time, the pottery industry in Britannia, which had produced pottery utensils in industrial quantities, also declined precitipitously.

Economically, the country collapsed. But in any such collapse, some people are affected more than others: wealth can insulate from many of the tribulations of the world.

But alongside the economic collapse, there was political disintegration.