Plague, Settlement and Structural Change at the Dawn of the Middle Ages
Scandia, Vol 59, Nr 1 (1993)
Something happened in late antiquity. Several elements in society underwent profound changes. According to many scholars, the most important feature was a demographic crisis. Various symptoms have been discussed: fewer slaves (from the second century AD), depopulation of frontier areas due to the wars (especially in the third century), the abandonment of agricultural areas and the spread of agri deserti (abandoned lands which could no longer yield taxes), the spread of the coloni (tenants attached to their lands by state decree and very dependent upon their landlords), the increasing number of Germanic soldiers in the army, the epibol system (originally a Ptolemaeic system that became widely used in the eastern empire: landowners were forced to take over evacuated lands close to their own and to pay taxes for these), etc.
The state wanted to maintain the level of agrarian production, and its failure is interpreted as a consequence of the demographic crisis. The shortage of manpower made it necessary to force people to remain where they were and to perform services needed in the empire, especially with regard to taxation. Professions were made hereditary. Eventually, many towns were ruralized or ceased to exist; the Roman empire in the west disintegrated and fell. Mostly, the research leading to conclusions such as these are based on studies of late Roman laws.