This chapter will deal with the origin of the people known as the Britons as defined under the headword ‘Briton, n.1. A member of one of the Brittonic-speaking peoples originally inhabiting all of Britain south of the Firth of Forth, and in later times spec. Strathclyde, Wales, Cornwall and Brittany’ in the OED, rather than the neologistic sense which has gradually displaced it and become more common since the late seventeenth century as applied to inhabitants or citizens of Great Britain or the United Kingdom. The principal argument here will be that this identity came into being in the course of Late Antiquity (i.e. c. AD 300-700).