[Tramonto]

Does anyone know the early history of this region or is it all speculation?

[Cronos]

No, not speculation. The FACT is that the Dacians were related to the Thracians (similar language if not the same language)

The Dacian wars of Trajan were pretty well documented (the Romans were really sticklers for noting down things!).

One hundred thousand male slaves were sent back to Rome; and in order to discourage future revolts Legio XIII Gemina and Legio V Macedonica were permanently posted in Dacia, the veterans of these legions were given land in Dacia and married Dacian women

When Rome fell, the people living there had been living for over 200 years and would have stuck on, even under Gothic kings (just like the Goths conquered Spain, but never made much of a difference to the local genetics, or just like the Bulgars in Bulgaria basically were just the elite rulers and they were soon subsumed amongst their Slavic people)