According to Greek mythology, Orestes, son of king Agamemnon, built this city as Orestias, at the confluence of the Tonsus (Toundja) and the Ardiscus (Arda) with the Hebrus (Maritza).
The new province of Thracia comprised the northwestern portion of the old province, i.e. the upper valley of the Hebrus river between Haemus and Rhodope and including Philippopolis, which had become the provincial capital in the early 3rd century.