While changes in urbanization, density and superficies of agglomerations in the western part of the Roman Empire can be easily pointed out, the fall of the Roman state was an important event along an evolution that began in the IIIrd century AD.

Several cities in Britain, Gaul (exception made of Provence) and partly so in Spain were reduced, productive and mercantile capabilities disappearing, and parts protected by new walls (built on the wake of raids and civil wars) significantly smaller than the former city (with some cases where intra muros neighborhood were partly inhabited themselves as in Amiens). This reduction led to two evolutions : the abandon of the planned grid an a ruralisation of elites; the public monumentality not being abandoned but transformed, either using new materials as wood, old monuments as quarries and especially with the appearance of Christian ensembles as churchs, cemeteries, monasteries, etc. Nevertheless, the cities closer to the limes seems to have particularly suffered from the crisis and raids already, several of them disappearing or heavily declining in Noricum (although they essentially survived upon the classical lines in Rhineland) without much respite in the IVth century.

In the Vth century, thus, the urban reality didn't as much disappeared than it was heavily transformed and adapted to the new realities, urban elites and middle-classes still holding out thanks to the existence of a Roman state whom fiscal needs, public service and mercantile safeguarding allowed and required their existence. The abandon or the disappearance of the imperial authority was really what crushed down cities, especially in Britain where urban maintenance became impossible in the matter of generations (towns weren't as much abandoned than "de-urbanized"), but as well in the Mediterranean part of the Empire where thus far preserved strong urban ensembles suffered a rapid change more so than cities set in the immediate periphery.

Due to the collapse of a fiscal network and an urban middle-class to entirely maintain them, the decline of imperial-wide trade and disappearance or change of trade roads, and in part due to the conflicts (especially in Italy with the Gothic Wars and subsequent conflicts with Lombards), Spanish and Italian cities went trough a long decline with several of them outright disappearing off the map, sometimes with a semi-urbanized population and elite remaining behind.

While the important decline of Rome is explainable as the result of a very large city depending on the existence of the Empire to maintain itself as such, its population declining being an "update" to its new quasi-provincial status; the urban decline for provincial cities still is perceptible along the history of the Late Empire (being understood that several of these cities could have harboured only some thousand denizens by the classical period already, in southern Gaul for instance). The structural changes of the IIIrd century and especially the Vth century as the Roman state collapsed being the main culprits, with depradation caused by civil wars and Barbarians being a matter of context.

Eventually, cities changed definition and outlook, but didn't vanished : where they were charaterized by their municipes and their middle-class, the presence of the bishop and defenses became more relevant with the Vth century, first in Gaul and Spain, eventually in Italy and Africa where the late imperial civilization was maintained for a longer time. Trade didn't as much disappeared than re-organized on different, impoverished lines : old cities as Massalia still prospered while new market places and harbours blossomed as Nice or Torcello. Populations refugeeing themselves, moving from cities to other, felt more protected, locations (e.g. Carpentras being left by its bishops and part of the population at the benefit of Venasque). What appears is a more polarized population without a strong middle-class, more fluctuating, gradual and precarious in its establishments (Ordezo/Eracliana being a short-lived agglomeration on this regard)