Dacia was the land of origin of the Dacians/Dutch/Deutsch.
Dacian Wars (101–102, 105–106) were two military campaigns fought between the Roman Empire and Dacia during the rule of the roman emperor Trajan.
Trajan marched on Dacia, conquered the Dacian capital and, to discourage future revolts, two legions were permanently posted in Dacia : XIII Gemina and V Macedonica.
Subsequently the massive wave of refuges moved toward north and north-west. Their name today survives in the modern names of the lands of Dutch and Deutsch-land.
The basis for this migration was the previous Dacian occupation of Slovakia in the era of Dacian king Burebista, whose campaigns outside Dacia have been dated 60–44 B.C.E., and were also noted through the location of Dacian cities on the lower Vistula river in Poland by Ptolemy and even as far as south and south-western Germany.
At length, with more info and evidence, here -> http://www.romanianhistoryandculture.com/daciansindenmark.htm#636399886