Dacians
Roman rule

Only about half part of Dacia then became a Roman province, with a newly built capital at Ulpia Traiana Sarmizegetusa, 40 km away from the site of Old Sarmisegetuza Regia, which was razed to the ground. The name of the Dacians' homeland, Dacia, became the name of a Roman province, and the name Dacians was used to designate the people in the region. Roman Dacia, also Dacia Traiana or Dacia Felix, was a province of the Roman Empire from 106 to 271 or 275 AD. Its territory consisted of eastern and southeastern Transylvania, and the regions of Banat and Oltenia (located in modern Romania). Dacia was organised from the beginning as an imperial province, and remained so throughout the Roman occupation. It was one of the empire's Latin provinces; official epigraphs attest that the language of administration was Latin. Historian estimates of the population of Roman Dacia range from 650,000 to 1,200,000.

Dacians that remained outside the Roman Empire after the Dacian wars of AD 101–106 had been named Dakoi prosoroi (Latin Daci limitanei), "neighbouring Dacians". Modern historians use the generic name "Free Dacians" or Independent Dacians. The tribes Daci Magni (Great Dacians), Costoboci (generally considered a Dacian subtribe), and Carpi remained outside the Roman empire, in what the Romans called Dacia Libera (Free Dacia). By the early third century the "Free Dacians" were a significantly troublesome group, by now identified as the Carpi. Bichir argues that the Carpi were the most powerful of the Dacian tribes who had become the principal enemy of the Romans in the region. In 214 AD, Caracalla campaigned against the Free Dacians. There were also campaigns against the Dacians recorded in 236 AD.

Roman Dacia was evacuated by the Romans under emperor Aurelian (ruled 271–5 AD). Aurelian made this decision on account of counter-pressures on the Empire there caused by the Carpi, Visigoths, Sarmatians, and Vandals; the lines of defence needed to be shortened, and Dacia was deemed not defensible given the demands on available resources. Roman power in Thracia rested mainly with the legions stationed in Moesia. The rural nature of Thracia's populations, and the distance from Roman authority, encouraged the presence of local troops to support Moesia's legions. Over the next few centuries, the province was periodically and increasingly attacked by migrating Germanic tribes. The reign of Justinian saw the construction of over 100 legionary fortresses to supplement the defence. Thracians in Moesia and Dacia were Romanized, while those within the Byzantine empire were their Hellenized descendants that had mingled with the Greeks.
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