A civilian settlement, or canabae, grew around the fortress. Chester Roman Amphitheatre south-west of the fortress is the largest known military amphitheatre in Britain. The civilian settlement remained after the Romans departed, eventually becoming the present-day city of Chester. There were peripheral settlements around Roman Deva, including Boughton, the source of the garrison's water supply, and Handbridge, the site of a sandstone quarry and the Minerva Shrine. The shrine is the only in situ, rock-cut Roman shrine in Britain.
The fortress contained barracks, granaries, headquarters, military baths, and an unusual elliptical building which had it been finished may have been intended to act as the governor of Britain's headquarters. Several factors including the uniqueness of the elliptical building, the method of construction, and the unusual size of the fortress – 20% larger than other Roman fortresses in Britain – suggest that it may have been intended as the base for a potential invasion of Ireland, and perhaps eventually to become the capital of the unified British Isles under Rome.
According to the 1st and 2nd century geographer Ptolemy, Deva was in the lands of the Cornovii. Their land bordered that of the Brigantes in the north and the Ordovices in the west and included parts of what is now Cheshire, Shropshire, and north Wales. When the Romans' treaty with the Brigantes – who occupied most of what is now Northern England – failed the Romans embarked on military conquest of the area. The campaigns were initially led by Sextus Julius Frontinus and later Gnaeus Julius Agricola. Their expansion into the north of Britannia during the reign of Vespasian meant that the Romans needed a new military base. Chester was a strategic site for a fortress, commanding access to the sea via the River Dee and dividing the Brigantes from the Ordovices. Legio II Adiutrix was sent to Chester and began the construction of a legionary fortress in the mid AD 70s.
The fortress was built on a sandstone bluff, overlooking the bridge crossing the river and close to the natural harbour which is today occupied by the Chester Racecourse. The bend in the River Dee provided protection from the south and the west. The river was navigable up to the sandstone ridge, so positioning the fortress beyond it would have made access to the harbour difficult. The fortress may have required up to 2,400,000 litres (530,000 imp gal) of water a day, supplied by fresh water piped in from natural springs in the suburb of Boughton 1.6 kilometres (1.0 mi) to the east.
Lead ingots discovered in Chester indicate that construction was probably under way by AD 74. There may already have been military buildings on the site, but if so they were demolished to allow the construction of the fortress. The first buildings were constructed from wood, probably for convenience. They were gradually replaced by more permanent structures built from locally quarried sandstone. Defence was provided by a 6-metre (20 ft) wide rampart and a ditch 3 metres (10 ft) wide and 1.5 metres (5 ft) deep. The rampart was made from turf laid over sand, clay, rubble, and layers of logs.