Isca Dumnoniorum settlement there (modern Caerleon) to be distinguished as "Isca Augusta", while the Devonian Isca was called "Isca Dumnoniorum": Usk of the Dumnonians. Exeter began as settlements on a dry ridge ending in a spur overlooking a navigable river teeming with fish, with fertile land nearby. Although there have been no major prehistoric finds, these advantages suggest the site was occupied early. Coins had been discovered from the Hellenistic kingdoms, suggesting the existence of a settlement trading with the Mediterranean as early as . This is disputed however by Prof T P Wiseman who alleges the hoard was not genuine. Following
Isca Augusta legion was needed to repel a potential invasion from the Continent. The stone from Isca may have been used for building defences on the south coast. There may still have been an occasional military presence as late as the early 4th century, but the fortress was probably later taken over by the people of the surrounding vicus. The basilica of the baths was used as a cattle pen. Recent finds suggest Roman occupation of some kind as late as AD 380. According to the Gildas (followed by Bede), Roman Caerleon was the site of two early Christian martyrdoms in Britain,