Several theories 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.