The breakdown of economic systems after the end of formal Roman administration in AD 410 makes it difficult to recognise very late Roman or early post-Roman deposits archaeologically, although new studies of the northern frontier region have identified certain artefact types, including military equipment, brooches and pottery, which have been recognised as continuing into the 5th century (see the papers in Collins and Allason-Jones 2010a). The scarcity of all types of these metal artefacts in the North West by contrast with east of the Pennines is attributed in part to much lower level of metal-detecting and excavation in the former region, but also biases in modern settlement (Collins and Allason-Jones 2010b, 134).
New evidence for occupation spanning the very late Roman to post-Roman period has come from some north-west military sites. The classic site is Birdoswald (Wilmott 1997) but in default of diagnostic artefacts careful stratigraphical analysis has shown that activity in this period persists in Lancashire forts, although only restricted areas of those sites have so far been examined. Some military sites certainly appear to have been occupied until the end of the Roman period (e.g. Ravenglass). Elsewhere, activity appears to continue into the post-Roman period at Ribchester (L) fort in excavations by UCLAN beginning in 2015, while a newly identified fort in West Lancashire (location confidential) has produced late deposits including an oven or hearth and stone platforms, the latter apparently for structural foundations, which overlie deposits with Crambeck/calcite-gritted wares dated AD 360-400+. Some structural platforms overlie internal fort roads. It remains uncertain how these places functioned, whether as lineal descendants of the military garrisons, with regional commanders protecting the local agricultural population in return for a customary levy, or as part of a wider administrative network, (Wilmott 2000).
The re-interpretation by Roger White of stratigraphic sequences in Chester at Abbey Green, Hunter Street and Hunter’s Walk highlights the problem of assigning accurate dates to activity which is broadly book-ended by the end of the Roman period and the medieval period. He argues that the presence of late Saxon pottery has been used to date features or phases often based on only slender associations and some activity may be 5th- or 6th-century in date, especially at Abbey Green which has East Mediterranean amphorae, North African pottery and horse-head military metalwork which would fit potentially into that period (2007, 187-189).
Part of the central area of the fort including the principia at Carlisle appears to have continued in use into the very late Roman period, and well into the 5th century, perhaps by non-military personnel, while adjacent streets were used as a market (McCarthy 2017, 10, and Table 2).
A late 4th or early 5th century military belt plate from Meols, a site with a coin list ending with Magnus Maximus (383-388), hints at late Roman military activity on the Irish Sea coast (Griffiths et al. 2007). This is one of the few sites in the North West where artefacts suggest continued activity through the early medieval period, supported by the hinterland distribution of 6th century Byzantine copper coins in north Wirral (Philpott in prep.). Other evidence is less coherent. An isolated pit, or possible kiln, at Nether Wasdale (C) provided a very late Roman or immediate post-Roman period date. This is exceptional in the context of the site and the region, and in association with the early medieval settlement containing evidence for metalworking the site is potentially of national significance (Oxford Archaeology North 2016). A late hoard of silver siliquae from Dutton (Ch), with coins minted in the mid 370s onwards, is the only siliqua hoard from the NW with a secure provenance (Oakden 2015, 52-53).
Many rural sites in the North West, where datable, have a peak in the 2nd century with a decline in the 3rd but very few can be proved to continue to the end of the Roman period (Nevell 2011, 48-50, fig. 3). Rural sites with late Roman or potential early post-Roman occupation include Mellor and Irby, Wirral; at the latter stratigraphic analysis, C14 dating and finds, including late 4th pottery, suggest occupation continued beyond the end of formal Roman occupation. Within the Saighton enclosures, the most clearly defined building (discussed above) consisted of a rectangular post-built structure, 14m by 6.5m in size and made up of ten roughly-paired posts, with a possibly internal partition and further external smaller posts. It appears to post-date the series of recorded sub-rectangular enclosures, and construction was dated by pottery to the late 4th century date, making it the latest identified feature (Wood 2016). On the face of it the decline in presumed agricultural units, and production, may be a consequence of lower demand due to a reduction in the size of the late Roman military garrison in the region, but a suggestion that this may be in part a reduction in visibility through a decline in engagement with the Roman money economy is also possible. Only tight sequences of radiocarbon dates will resolve the questions over the duration of site occupation during materially poor periods.