A member of a group of west European peoples, including the pre-Roman inhabitants of Britain and Gaul and their descendants, especially in Ireland, Scotland, Wales, Cornwall, Brittany, and the Isle of Man. The Celtic language is a sub-group of the Indo-European language group, divided into two groups, Goidelic (consisting of Irish, Scots Gaelic, and Manx) and Brythonic (consisting of Welsh, Cornish, and Breton).

The Celts occupied a large part of Europe in the Iron Age. Their unity is recognizable by common speech and common artistic tradition, but they did not constitute one race or group of tribes ethnologically. The origins of their culture can be traced back to the Bronze Age of the upper Danube in the 13th century bc, with successive stages represented by the urnfield and Hallstatt cultures. Spreading over western and central Europe from perhaps as early as 900 bc, they reached the height of their power in the La Tène period of the 5th–1st centuries bc. The ancients knew them as fierce fighters and superb horsemen, with savage religious rites conducted by the Druid priesthood. They were farmers, who cultivated fields on a regular basis and had developed ox-drawn ploughs to use in place of manual implements, a revolutionary advance that permanently affected people’s way of life. But Celtic political sense was weak and the numerous tribes, continually warring against each other, were crushed between the migratory Germans and the power of Rome, and were ejected or assimilated by the former or conquered outright by the latter.