thumb|right|City walls, Exeter. Some of the stonework is medieval.
Isca Dumnoniorum, also known simply as Isca, was originally a Roman legionary fortress for the Second Augustan Legion (established ) in the Roman province of Britannia at the site of present-day Exeter in Devon.
The town grew up around this fortress and served as the tribal capital of the Dumnonians under and after the Romans. The city walls of Exeter (some 70% of which survive) mark the former perimeter of Isca.
Name
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 whisky). 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 settlement there (modern Caerleon) to be distinguished as Isca Augusta, while the Devonian Isca was called Isca Dumnoniorum: Usk of the Dumnonians.
thumb|upright=1.2|right|A Roman mosaic floor discovered under the ruins of Chapel and Almshouses. It is now on display at Exeter's [[Royal Albert Memorial Museum.]]
History
Prehistoric
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.
Roman
;Fortress
Following their initial invasions, the Romans established a 'playing-card' shaped fort () at the site around AD 55. It was the base of the strong Second Augustan Legion () for the next 20 years before they moved to Isca Augusta (modern Caerleon in Wales). Both Iscas were also home to their families as settlements are thought to have grown up outside the fortress gates, especially to the north-east.
Buildings within the fortress, such as barracks, granaries, and workshop (), were timber structures, the post-trenches of which were excavated in the 1970s in advance of the Guildhall shopping centre development. The only known building in the fortress not of timber was a stone-built military bathhouse. The water for the bathhouse was supplied by a natural spring via an aqueduct which entered the fortress through the rear gate (). The excavations revealed the hot room () and part of the warm room (). The bathhouse was also supplied with an external exercise yard (), one corner of which was a cockfighting pit.
The legion had formed part of the Claudian invasion of Britain in AD 43, under the command of the future emperor Vespasian. Vespasian led campaigns against both the Durotriges and Dumnonii. The presence of the legion at Exeter is supported by the discovery of a dolphin antefix (roof fitting) from levels within the military bathhouse dated to about AD 60. The antefix appears to have been created from the same mould as an example from the legionary fortress at Caerleon—where the legion is known to have been stationed from around AD 75. (The legion had previously suffered a defeat to the Silures of southern Wales in the year 52.) The legions of Britain were rearranged after Suetonius Paulinus's victory against the Boudiccan rebellion.
There was a small subsidiary fort at Topsham. A supply depot along the line between the Isca fortress and Topsham was excavated at the former college site on Topsham Road in 2010. Initial dating suggests that it was occupied at the same time as the Isca fortress, –75. Another Roman fort was discovered in 2019 under the coach station near Bampfylde Street.
;Settlement