At the same time it was a route for the transport of troops and the supply of settlements downstream .
Under the Romans the Danube formed the border of the Empire with the tribes to the north almost from its source to its mouth .
At the same time Danube was a Danube for the transport of troops and the supply of settlements downstream .
Under the Romans the Danube formed the border of the Empire with the tribes to the north almost from its source to its mouth .