Dacia Traiana in the context of "Decebalus"

Several theories, in great extent mutually exclusive, address the issue of the origin of the Romanians. The Romanian language descends from the Vulgar Latin dialects spoken in the Roman provinces north of the "Jireček Line" (a proposed notional line separating the predominantly Latin-speaking territories from the Greek-speaking lands in Southeastern Europe) in Late Antiquity. The theory of Daco-Roman continuity argues that the Romanians are mainly descended from the Daco-Romans, a people developing through the cohabitation of the native Dacians and the Roman colonists in the province of Dacia Traiana (primarily in present-day Romania) north of the river Danube. The competing immigrationist theory states that the Romanians' ethnogenesis commenced in the provinces south of the river with Romanized local populations (known as Vlachs in the Middle Ages) spreading through mountain refuges, both south to Greece and north through the Carpathian Mountains. Other theories state that the Romanized local populations were present over a wide area on both sides of the Danube and the river itself did not constitute an obstacle to permanent exchanges in both directions; according to the "admigration" theory, migrations from the Balkan Peninsula to the lands north of the Danube contributed to the survival of the Romance-speaking population in these territories.

Political motivations—the Transylvanian Romanians' efforts to achieve their emancipation, Austro-Hungarian and Romanian expansionism, and Hungarian irredentism—influenced the development of the theories, and "national passions" still color the debates. In 2013, authors of The Cambridge History of the Romance Languages came to the conclusion that the "historical, archaeological and linguistic data available do not seem adequate to give a definitive answer" in the debate. Their view was accepted by scholars contributing to The Oxford Guide to the Romance Languages, published in 2016, which reiterates that "the location and extent of the territory where "Daco-Romance" originated" is uncertain.

Dacia Aureliana was a province in the eastern half of the Roman Empire established by Roman Emperor Aurelian in the territory of former Moesia Superior after his evacuation of Dacia Traiana beyond the Danube in 271. Between 271/275 and 285, it occupied most of what is today northwestern Bulgaria and eastern Serbia. Its capital was in Serdica (modern Sofia).

This province was populated with a part of the former inhabitants of Dacia Traiana. It is written in Eutropius' work: Abridgment of Roman History (9:15):