Between 907 and 921 further forts were built over an area which stretched from north-east Wales to Manchester. Chester thus became the focus of complex garrisoning arrangements, initially to monitor Viking settlement. Cestrians may at first have welcomed Æthelflæd: she was half Mercian and had married Æthelred (d. 911), the ruler (patricius) of Mercia, whose origins are unknown but who was almost certainly descended from the Mercian kings. After Æthelflæd's death in 918, however, her brother King Edward the Elder seized and imprisoned the Mercian heir Ælfwynn, Æthelred and Æthelflæd's daughter. That coup d'état, essentially a West Saxon takeover of the remains of Mercia, was clearly much resented. The king's visits to Cheshire and north Wales in 919 and 921, which resulted in the building of three new burhs, may well have been as much to suppress the consequent local unrest as to deal with the Vikings.
Eventually, in 924, the men of Chester revolted in alliance with the Welsh. Edward went again to the North-West, took and garrisoned the city, but died shortly afterwards near by at Farndon. At the time Chester was thus clearly seen as a military centre of great importance, whose contacts with the Hiberno-Norse and north Wales rendered it particularly sensitive.
The accession of Æthelstan in 924 restored the burh's fortunes. The king, who had been brought up at the court of his aunt Æthelflæd, was popular with and well disposed towards his Mercian subjects. During his reign Chester retained its strategic significance because of its command over the route to Dublin and its proximity to Wales, whose princes' relations with the West Saxons were always ambiguous. In 937 it may well have sheltered Æthelstan before his victory over the Scots and the Dublin Norsemen at 'Brunanburh' (probably nearby Bromborough), and it was again crucially placed in 942 when there was collusion between the Welsh and the Scandinavian kingdom of York during King Edmund's campaign against the latter.
Chester was the administrative as well as the military centre for the district involved in its maintenance as a royal fortress. Above all, it was the site of the court for a shire which may have originated in the early 10th century and certainly existed by 980. The area involved was large: it presumably comprised the 12 hundreds of Cheshire listed in the Domesday Survey, and possibly for a while included south Lancashire as well. The city had an important mint, whose activities, at least in the earlier 10th century, were almost certainly supervised by royal officials, and whose exceptional productivity is a clear indication that Chester mattered to kings. Its fortunes mirrored those of the city. Having flourished under Æthelflæd, when it produced coins of distinctive north-western design, it reverted to more standard types when Edward the Elder took over, probably because of the intrusion of new moneyers from the South. Under Æthelstan, when coins first had a securely identifiable Chester mint-signature, a distinctive type was again issued, one which eschewed the portrait head of the alien West Saxon kings. Remarkably, the mint then became the most prolific centre of coin production in England, rivalling London in importance.
The settlement may well have extended across the river into Handbridge, which in 1086 was assessed for tax in carucates rather than the hides normal in Cheshire. Carucates occurred elsewhere in the county in association with Scandinavian place-names, and appear to be evidence of Scandinavian settlement.
The new burh was also the centre of important ecclesiastical developments. Late and unreliable traditions alleged that the body of St. Werburg was carried to Chester in 875 and installed in a minster refounded in her honour. The minster undoubtedly existed by 958, and on balance it seems likely that Æthelflæd was responsible for the translation and refoundation after 907, since she had engaged in similar activities elsewhere. By the 13th century St. Werburgh's was closely associated with the cult of St. Oswald, also favoured by Æthelflæd and perhaps also introduced by her to Chester. The installation of such respected Mercian relics suggests that the burh was regarded not simply as a garrisoned fortress but as a major centre of authority, the focus of attempts to conciliate local resentment of the West Saxon incomers.
In 1719 the separate parish of Sunderland was carved from the densely populated east end of Bishopwearmouth, to serve the port. Local government was divided between the three churches (Holy Trinity, Sunderland, St. Michael's, Bishopwearmouth, and St. Peter's, Monkwearmouth) and when cholera broke out in 1830 the "select vestrymen", as the church councilmen were called, showed themselves completely unable to understand and cope with the epidemic. Ships were built on the Wear from at least 1346 onwards and by the mid-eighteenth century Sunderland was probably the chief ship-building town in the country. The Port of Sunderland was significantly expanded in the 1850s. Sunderland developed on plateaux high above the river, and so never suffered from the problem of allowing people to cross the river without interrupting the passage of high masted vessels. Staindrop is situated to the east of Barnard Castle, on the north side of the River Tees, opposite Startforth.