Migrants or slaves?
The movement of people during the classical period has always been a fascinating subject to me.
A while back I did a lot of study on Romania (Roman Dacia), and that province was considered the “California” of the Roman Empire in the 2nd Century AD. The region was so thoroughly Latinized that it is the only nation east of Italy that still retains a Romance language.
I have traced my family back two thousand years and found them living in Eastern Europe at that time. As the centuries passed they moved further west until they eventually settled in what is now Denmark. Some of them continued on to Norway and ended up in Scotland. Others went to Austria and ended up in England. The ones who came to Ireland started out in Turkey.
Rome spent serious time, blood, and treasure to conquer and hold Dacia down over a couple of centuries; Aurelian (one of my favorite emperors) gave it up, resettling Romans from Dacia into territories s of the Danube. If not for Aurelian, there would have been no successors, Rome would have been finished a couple hundred years early, there would have been no Byzantine empire as such, and European, n African, and Near East history (at least) would have been quite different.
There's no controversy that the Roman Empire made it fairly simple for ethnic groups to relocate within and outside the borders (people from India lived in Rome, Romans joined Greeks already living in India, etc), there's been some DNA studies of human remains of that era, just not from Italy. There are very few known human remains from Roman Italy, and most of them haven't been studied at all (DNA studies don't always work, there's not enough material to study).