The Boian culture originated on the Wallachian Plain north of the Danube River in southeastern Romania. At its peak, the culture expanded to include settlements in the Bărăgan Plain and the Danube Delta in Romania, Dobruja in eastern Romania and northeastern Bulgaria, and the Danubian Plain and the Balkan Mountains in Bulgaria. The culture's geographical extent went as far west as the Jiu River on the border of Transylvania in south-central Romania, as far north as the Chilia branch of the Danube Delta along the Romanian border with Ukraine and the coast of the Black Sea, and as far south as the Rhodope Mountains and the Aegean Sea in Greece.