Migration of populations was also a social and military phenomenon which Rome was regularly subject to: it wasn’t always Roman aggression beyond her confines but also not infrequent cases of external peoples and tribes organising incursions into Roman territory. A famous example of this was when Rome was still a republic, with the incursions of the migrant Germanic tribes of the Cimbri and Teutones (eventually defeated by general Marius).
Equally important is a clear definition of what we might mean by immigration and of what we mean by “Rome”. Ie is immigration to be considered movement of people from outside roman dominions inwards, do we include flows of people from conquered states, including slaves? Should we also consider inflow of people from the countryside into the city: the huge size of ancient Rome at the height of the empire is in itself an ample evidence of the enormous population flows involved through time. Last but not least should we include the increasing number of peoples which under the principate (empire) were granted full Roman citizenship?
Immigration was also one of the aspects which characterised the decline of the roman empire. Germanic tribes, under pressure from eastern threats and hunger at first asked and once refused eventually forced their way into Roman territory. Similarly there is the so-called “Rescripts of Honorius” in which Emperor Honorius essentially tells the Britons to look after themselves: the empire’s resources were stretched and the outer confines became less secure.
Roman border policy was an extremely important aspect of the empire’s wellbeing. For at least two centuries from the time of Emperor Augustus onward the attitude was substantially one of non aggressive imperialism to ensure border security for its overstretched resources except perhaps in some areas where campaigns might be conducted to reinforce or straighten/shorten a border. Particular attention and focus was paid on the borders with the Germanic tribes along the Danube and one those in the region of Syria with the Parthian empire and over time a system of limites or limes (fortified walls and ditches) was constructed of which Hadrian’s wall in Britain is a famous example.
Chroniclers like Tacitus give some sense of the general approach adopted by various emperors when he describes that some tribes even went as far as sending envoys to Rome asking to be included within the empire’s limits but were refused on the basis of the resource required to defend regions and territories which might essentially be considered poor and profitless. Rome did however make great use of friendly states and tribes just across its borders as a means of reinforcing peace across them – a practice generally known as “divide et impera” (divide and rule).
A sense of the volume of immigration (at least into the city of Rome, if not the empire – see above) can be had by considering the growing size of ancient Rome which at its peak had nigh on 1M citizens, be they plebeians, freed slaves, foreigners or others.
What is particular important to consider is the role which immigration and population size played on the Roman economy. Enormous efforts both financial and military were put behind the necessity of feeding the burgeoning population of the city through vast grain imports from areas such as Sicily and Egypt, cities such as Alexandria. Rome’s political, military and financial success, coupled with its incomparable infrastructure made it the target for many people in search of fortune. This enormous plebeian population, particularly when civili status was extended to greater number of provinces, meant a need to feed such people, at public expense, which in turn implied an increasingly negative balance of trade. Furthermore these people found it extremely difficult to find work, given the excessive supply of labour, the pay was increasingly low, forcing people into slavery, making social unrest a continuing preoccupation for the governing authorities and as such hindering incentives for technological advancements which might have generated higher efficiency and productivity.
Towards the end of the empire farmers began to abandon the fields on the border lands which were prone to skirmishes and raids, in preference for a safer life in the city. Thepopulation at the time of the fall of Rome dropped to somewhere in the region of 2-500,000 by the time of the fall of the roman empire and a tenth of that by the first millennium.
The Phenomenon of Immigration as part of Roman Colonisation
When considering population movements in the ancient Roman empire we mustn’t forget emigration of Roman citizens to the colonies. Land was a regular means of remuneration for Roman soldiers although it might mean foregoing one’s right to be considered a Roman citizen.
The creation of a new colony or indeed of recognising a city’s status of independence implied investment which integrated Roman custom with local customs, the introduction of some roman religious practices without necessarily destroying the identity of what was already there and generally creating a blend of the two cultures. A charter would be written giving the town or city its special status as self governing entities, magistrates would be elected both for public and religious duties, investments would be made to construct and expand the city and to celebrate public games. This process is generally referred to as “Romanisation”.
An example of one such charter is from the colony of Urso in 44BC (modern Osuna, in Spain). Another example with similar approach (with Roman settlers and charter) is Pompeii.