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
Isca Augusta River Usk. The suffix "Augusta" appears in the Ravenna Cosmography and was an honorific title taken from the legion stationed there. The place is commonly referred to as "Isca Silurum" to differentiate it from Isca Dumnoniorum and because it lay in the territory of the Silures tribe. However, there is no evidence that this form was used in Roman times. The later name, "Caerleon", is derived from the Welsh for "fortress of the legion". Isca was founded in AD 74 or 75 during the final campaigns by Governor Sextus Julius Frontinus against the fierce native tribes of western Britain, notably