What did medieval writers mean when they referred to 'Britain'? They seem to have had a fairly clear idea of the geographical location and dimensions of the whole island, and were fond of repeating the description by Gildas in the early sixth century: 'The island of Britain, situated on almost the utmost border of the earth, towards the south and west ... stretches out from the southwest towards the North Pole, and is eight hundred miles long and two hundred broad, except where the headlands of sundry promontories stretch farther into the sea.'
But Britain was always more than an area of land, and from earliest times, the term 'Britain' has had two distinct meanings: the whole island, and the southern part which formed the Roman province of Britannia. Gildas himself referred to its twenty-eight cities, and his book, entitled On the Ruin of Britain, is about the downfall of a realm and its people. It is here, when we come to consider the various real and imagined political domains called 'Britain' in ancient and medieval times, that things become complicated. Though the Roman general Agricola got as far north as the Tay, and possibly Aberdeenshire, in the first century AD, most of what is now Scotland was never included in Britannia, whose northern limit was marked for most of its history by Hadrian's Wall, between the Tyne and the Solway. The farthest north that Roman rule ever extended was the Antonine Wall, between the Forth and the Clyde, and Gildas himself seems to have thought of this as the northern limit of British territory.
Bede, writing more than a 150 years after Gildas, made an explicit distinction between 'Britain' and 'the British part of it', explaining that the Britons were harassed by 'two extremely fierce races from over the waters, the Irish from the west and the Picts from the north'. He comments that 'we call them races from over the waters, not because they dwelt outside Britain but because they were separated from the Britons by two wide and long arms of the sea, one of which enters the land from the east, the other from the west, though they do not meet.' These 'arms of the sea' are clearly the Firths of Forth and Clyde. The ninth-century History of the Britons also seems to give us two Britains. First there is the island which is eight hundred miles long and two hundred wide, and is inhabited by the Scots, Picts, Saxons and Britons. But when the anonymous author went on to name the thirty-three cities of Britain, the most northerly of these appears to be Dumbarton on the Clyde (or, in one version, Carlisle), suggesting there was another, non-British, kingdom to the north. The same distinction was maintained in the Northern Version of the Anglo-Saxon Chronicle, which began with a preface repeating Bede's account of the dimensions of Britain, and went on to explain that 'the Picts went and took possession of the northern part of the island; and the Britons had the southern part.'
The first English king to claim the overlordship of Britain was Edwin of Northumbria (c. 586-633). The fifth in Bede's list of the seven kings who ruled 'over all the southern kingdoms, which are divided from the north by the river Humber', Edwin is said to have had even greater power than those who came before him, ruling over 'all the inhabitants of Britain, English and Britons alike, except for Kent only'. Bede's account of the sixth and seventh kings makes it plain that 'Britain' here must mean something considerably less than the whole island, because he says that while Edwin's successor Oswald ruled 'within the same bounds', his brother Oswiu extended his dominion and 'overwhelmed and made tributary even the tribes of the Picts and Irish who inhabit the northern parts of Britain'. Once more, Bede seems to be thinking in terms of two Britains: the territory excluding 'the northern parts', as ruled by Edwin and Oswald; and the whole island, of which Oswiu was overlord. …