Isca Dumnoniorum but seems to have gone into decline prior to the Roman withdrawal from Britain . The name "Isca Dumnoniorum" is a Latinization of a native Brittonic name describing flowing water, in reference to the River Exe. More exactly, the name seems to have originally meant "full of fish" (cf. Welsh "pysg", "fish"), although it came to be a simple synonym for water (cf. Scottish whiskey). This is also reflected in the modern Welsh name for Exeter: "Caerwysg" meaning "fortified settlement on the river Uisc". The same name was used for the River Usk (modern ) in southern Wales, causing the
Celtic language decline in England England begin to be attested from around 670, pre-eminently in Anglo-Saxon charters; they have been intensively surveyed by the English and Scottish Place-Name Societies. Except in Cornwall, the vast majority of place-names in England are easily etymologised as Old English (or Old Norse, due to later Viking influence), demonstrating the dominance of English across post-Roman England. This has traditionally been seen as evidence for a cataclysmic cultural and demographic shift at the end of the Roman period, in which not only the Brittonic and Latin languages, but also Brittonic and Latin place-names, and even Brittonic- and Latin-speakers, were swept away.