The term Romano-British describes the Romanised culture of Britain under the rule of the Roman Empire, when Roman and Christian culture had extensively entered into the life of the native Brythonic, Pictish and perhaps Gaelic -speaking peoples of Britain.

One vector of Roman influence into British life was the grant of Roman citizenship. At first this grant went out very selectively: to the council members of certain classes of towns, which Roman practice made citizens; to veterans, either legionaries or soldiers in auxiliary units; and to a number of natives whose patrons were able to obtain it for them -- some of the local Celtic kings, such as Togidubnus, received citizenship in this manner. However, the number of citizens steadily increased over the years, as people inherited citizenship and more grants were made. Eventually all people who were not slaves or freed slaves were granted citizenship by the Constitutio Antoniniana in AD 212.

The other inhabitants of Britain, who did not enjoy citizenship, were Peregrini, who continued to live under the laws of their ancestors. The principal handicaps were that they could not:

• own land with an Italic title,
• serve as a Legionaire in the army (although they could serve in an auxiliary unit, and become a Roman citizen upon discharge) nor could they
• usually inherit from a Roman citizen

But for the vast number of British inhabitants, who were peasants tied to the soil, citizenship would not dramatically alter daily operation of their lives.

Britain was also independent of the rest of the Roman Empire for a number of years, first as a part of the Gallic Empire, then a couple of decades later under the usurpers Carausius and Allectus.

Christianity came to Britain in the third century. One early figure was Saint Alban, who was martyred near the Roman town of Verulamium, on the site of the modern St Albans, by tradition during the reign of the emperor Decius.

After the withdrawal of Roman troops in the reign of the emperor Honorius the Romano-British were forced to defend their Romanised civilisation with their own forces. The depredations of the Picts from the north and Scotti (Scots) from Ireland forced them to seek help from pagan Germanic tribes of Angles, Saxons and Jutes, who decided to settle. However, the Germanic tribes turned on their hosts, eventually confining the Romano-British culture to the western part of the island: Wales, Devon and Cornwall, Strathclyde, Cumbria and Elmet, while in Scotland after gains in influence by the Scots it became confined mostly to the east. Many Romano-British migrated to Brittany and possibly Ireland and Galicia in Northern Spain.

The struggles of this period have given rise to the legends of Uther Pendragon and King Arthur. It is sometimes said that Ambrosius Aurelianus, the leader of the Romano-British forces, was the model for the former, and that Arthur's court of Camelot is an idealised Welsh memory of pre-Saxon Romano-British civilisation.

See: Roman Britain, Roman sites in the United Kingdom