Roman Britain about the year 410 CE, showing the Brythonic tribes in red.
Ancalites (Hampshire and Wiltshire, England)
Attacotti (Scotland or Ireland)
Atrebates (an important tribe of Southern England)
Belgae (Wiltshire and Hampshire) - according to some, they may have been Germanic[1]
Bibroci (Berkshire, England)
Brigantes (an important tribe in most of Northern England) and in the south-east corner of Ireland)
Caereni (far western Highlands)
Caledones (along the Great Glen)
Cantiaci (present-day Kent which preserves the ancient tribal name)
Carnonacae (western Highlands)
Carvetii (Cumberland)
Cassi (England)
Cateni (north and west of Sutherland) - they gace the county its Gaelic name Cataibh
Catuvellauni (Hertfordshire) - neighbours of the Iceni, they joined in their rebellion
Corieltauvi (Leicestershire)
Corionototae (Northumberland)
Corieltauvi (East Midlands including Leicester)
Cornovii (Cornish)
Cornovii (Midlands)
Cornovii (Caithness)
Creones (Argyll)
Deceangli (Flintshire)
Decantae or Ducantae (eastern Ross and Black Isle)
Demetae (Dyfed)
Dobunni (Cotswolds and Severn valley)
Dumnonii or Damnonii, Domnainn) (Devon, Cornwall, Somerset, Strathclyde, and Connacht)[2][3][4][5]
Durotriges (Dorset, south Somerset, south Wiltshire)
Epidii (Kintyre and neighboring islands)
Gangani (Ll?n Peninsula)
Horestiani (Fife, Scotland)
Iceni (East Anglia) - under Boudica, they rebelled against Roman rule
Lugi (southern Sutherland)
Scotti (western portion of Scotland)
Segontiaci (England)
Selgovae (north of Dumfries and Galloway)
Ordovices (Gwynedd) - they waged guerrilla warfare from the north Wales hills
Parisii (East Riding of Yorkshire and Humberside)
Regnenses (Hampshire)
Setantii (Lancashire)
Silures (Gwent) - also resisted the Romans in present-day south Wales
Smertae (central Sutherland)
Taexali (Grampian)
Trinovantes (Essex) - neighbours of the Iceni, they joined in their rebellion
Uluti or Volunti (north-east of Ireland and Lancashire - they gave their name to Ulster
Vacomagi (in and around the Cairngorms)
Venicones (Fife and south-east Tayside in Scotland
Votadini (north-east England and south-east Scotland - they later formed Gododdin