About the fifth century B.C., when the population of the Balkan-Carpathian region consisted of various tribes belonging to the Indo-European family, the northern portion of the Balkan peninsula was conquered by the Thracians and the Illyrians. The Thracians spread north and south, and a branch of their race, the Dacians, crossed the Danube. The latter established themselves on both sides of the Carpathian ranges, in the region which now comprises the provinces of Oltenia (Rumania), and Banat and Transylvania (Hungary). The Dacian Empire expanded till its boundaries touched upon those of the Roman Empire. The Roman province of Moesia (between the Danube and the Balkans) fell before its armies, and the campaign that ensued was so successful that the Dacians were able to compel Rome to an alliance. Two expeditions undertaken against Dacia by the Emperor Trajan (98-117) released Rome from these ignominious obligations, and brought Dacia under Roman rule (A.D. 106). Before his second expedition Trajan erected a stone bridge over the Danube, the remains of which can still be seen at Turnu-Severin, a short distance below the point where the Danube enters Rumanian territory. Trajan celebrated his victory by erecting at Adam Klissi (in the province of Dobrogea) the recently discovered _Tropaeum Traiani_, and in Rome the celebrated ‘Trajan’s Column’, depicting in marble reliefs various episodes of the Dacian wars. The new Roman province was limited to the regions originally inhabited by the Dacians, and a strong garrison, estimated by historians at 25,000 men, was left to guard it. Numerous colonists from all parts of the Roman Empire were brought here as settlers, and what remained of the Dacian population completely amalgamated with them. The new province quickly developed under the impulse of Roman civilization, of which numerous inscriptions and other archaeological remains are evidence. It became one of the most flourishing dependencies of the Roman Empire, and was spoken of as _Dacia Felix_. About a century and a half later hordes of barbarian invaders, coming from the north and east, swept over the country. Under the strain of those incursions the Roman legions withdrew by degrees into Moesia, and in A.D. 271 Dacia was finally evacuated. But the colonists remained, retiring into the Carpathians, where they lived forgotten of history.