The peoples of these islands were called the Πρεττανοί (Prettanoi), Priteni, Pritani or Pretani.The group included Ireland, which was referred to as Ierne (Insula sacra “sacred island” as the Greeks interpreted it) “inhabited by the race of Hiberni” (gens hibernorum), and Britain as insula Albionum, “island of the Albions”.The extent of their territory before and during the Roman period is unclear, but is generally believed to include the whole of the island of Great Britain, at least as far north as the Clyde-Forth isthmus, and if the Picts are included as Brittonic speaking people as they more usually are, the entirety of Great Britain.
Part of the Pictish territory was eventually absorbed into the Gaelic kingdoms of Dál Riata and Alba, which became Scotland.
The Isle of Man, Shetland, Hebrides and the Orkney islands were originally inhabited by Britons also, but eventually became respectively Manx and Scots Gaelic speaking territories, while the Scilly isles and Anglesey (Ynys Mon) remained Brittonic and the originally Brittonic Isle of Wight was taken by Anglo-Saxons. The British tribes opposed the Roman legions for many decades, but by 84 AD the Romans had decisively conquered southern Britain and had pushed into Brittonic areas of what would later become northern England and southern Scotland.
Although the native Britons south of Hadrian’s Wall mostly kept their land, they were subject to the Roman governors, whilst the Brittonic-Pictish Britons north of the wall remained fully independent.
The Roman Empire retained control of “Britannia” until its departure about AD 410, although some parts of Britain had already effectively shrugged off Roman rule decades earlier.
The term Pritani may have reached Pytheas from the Gauls, who possibly used it as their term for the inhabitants of the islands.
The Anglo-Saxon Chronicle, which was originally compiled by the orders of King Alfred the Great in approximately 890, and subsequently maintained and added to by generations of anonymous scribes until the middle of the 12th century, starts with this sentence: “The island Britain is 800 miles long, and 200 miles broad, and there are in the island five nations: English, Welsh (or British, including the Cornish), Scottish, Pictish, and Latin.The first inhabitants were the Britons, who came from Armenia, and first peopled Britain southward.” (“Armenia” is possibly a mistaken transcription of Armorica, an area in northwestern Gaul including modern Brittany.) The Latin name in the early Roman Empire period was Britanni or Brittanni, following the Roman conquest in AD 43.The Welsh word Brython was introduced into English usage by John Rhys in 1884 as a term unambiguously referring to the P-Celtic speakers of Great Britain, to complement Goidel; hence the adjective Brythonic referring to the group of languages.With the beginning of Anglo-Saxon settlement and Gaelic Scots in the 5th century, the culture and language of the Britons fragmented and much of their territory was taken over by the Anglo-Saxons and Scots Gaels.The extent to which this cultural and linguistic change was accompanied by wholesale changes in the population is still a matter of discussion.After the Acts of Union 1707, the terms British and Briton came to be applied to all inhabitants of the Kingdom of Great Britain and its empire.