Stretching from the Atlantic to the Tigris, the Roman empire contained approximately 65 million inhabitants. The Roman elites were bilingual. They spoke both Latin and Greek.
The Romans remained in Britain from 43 AD to 410 AD.
Roman Britain was ethnically diverse. This means that the population was composed of many different ethnic backgrounds. Many peoples incorporated into the empire continued to speak their native tongue.
Occupying legions were drawn from other parts of the Empire. Romans believe that if you were a citizen you had a duty to fight for your state. If you fought you were entitled to political rights.
Slaves, wives and tradespeople from the empire’s legions played a role in diversifying different corners of the empire by settling in the far-flung locations conquered by the Romans. In other words, immigration.
Many sea-going and land-based merchants and trades people went voluntarily as their occupations required or were posted by employers/benefactors to positions away from their native towns.
London, called Londinium, was founded by the Romans in 47 AD. As a major trading centre, the city was especially diverse. People lived, worked and died together from all over.