Main article: Insular Celts
All living Celtic languages today belong to the Insular Celtic languages, derived from the Celtic languages
spoken in Iron Age Britain and Ireland.[116] They separated into a Goidelic and a Brittonic branch early on.
By the time of the Roman conquest of Britain in the 1st century AD, the Insular Celts were made up of
the Celtic Britons, the Gaels (or Scoti), and the Picts (or Caledonians).[ citation needed ]
Linguists have debated whether a Celtic language came to the British Isles and then split, or whether the
two branches arrived separately. The older view was that Celtic influence in the Isles was the result of
successive migrations or invasions from the European mainland by diverse Celtic-speaking peoples over
several centuries, accounting for the P-Celtic vs. Q-Celtic isogloss. This view has been challenged by the
hypothesis that the islands' Celtic languages form an Insular Celtic dialect group.[117] In the 19th and 20th
centuries, scholars often dated the "arrival" of Celtic culture in Britain (via an invasion model) to the 6th
century BC, corresponding to archaeological evidence of Hallstatt influence and the appearance
of chariot burials in what is now England. Cunliffe and Koch propose in their newer #'Celtic from the
West' theory that Celtic languages reached the Isles earlier, with the Bell Beaker culture c.2500 BC, or
even before this.[118][119] More recently, a major archaeogenetics study uncovered a migration into
southern Britain in the Bronze Age from 1300 to 800 BC.[120] The newcomers were genetically most
similar to ancient individuals from Gaul.[120] From 1000 BC, their genetic marker swiftly spread through
southern Britain,[121] but not northern Britain.[120] The authors see this as a "plausible vector for the
spread of early Celtic languages into Britain".[120] There was much less immigration during the Iron Age,
so it is likely that Celtic reached Britain before then.[120] Cunliffe suggests that a branch of Celtic was
already spoken in Britain, and the Bronze Age migration introduced the Brittonic branch.[122]
Like many Celtic peoples on the mainland, the Insular Celts followed an Ancient Celtic religion overseen
by druids. Some of the southern British tribes had strong links with Gaul and Belgica, and minted their
own coins. During the Roman occupation of Britain, a Romano-British culture emerged in the southeast.
The Britons and Picts in the north, and the Gaels of Ireland, remained outside the empire. During
the end of Roman rule in Britain in the 400s AD, there was significant Anglo-Saxon settlement of eastern
and southern Britain, and some Gaelic settlement of its western coast. During this time, some Britons
migrated to the Armorican peninsula, where their culture became dominant. Meanwhile, much of
northern Britain (Scotland) became Gaelic. By the 10th century AD, the Insular Celtic peoples had
diversified into the Brittonic-speaking Welsh (in Wales), Cornish (in Cornwall), Bretons (in Brittany) and
Cumbrians (in the Old North); and the Gaelic-speaking Irish (in Ireland), Scots (in Scotland) and Manx (on
the Isle of Man).[ citation needed ]
Classical writers did not call the inhabitants of Britain and Ireland Celtae or Κελτοί ( Keltoi ),[5][8][9] leading
some scholars to question the use of the term 'Celt' for the Iron Age inhabitants of those
islands.[5][8][9][10] The first historical account of the islands was by the Greek geographer Pytheas, who
sailed around what he called the "Pretannikai nesoi" (the "Pretannic isles") around 310–306 BC.[123] In
general, classical writers referred to the Britons as Pretannoi (in Greek) or Britanni (in Latin).[124] Strabo,
writing in Roman times, distinguished between the Celts and Britons.[125] However, Roman
historian Tacitus says the Britons resembled the Celts of Gaul in customs and religion.[11]