To the south, it has been argued that the ancient Thracian language was a dialect of Dacian, or vice versa, and that therefore the Dacian linguistic zone extended over the Roman province of Thracia, occupying modern-day Bulgaria south of the Balkan Mountains, northern Greece and European Turkey, as far as the Aegean sea. But this theory, based on the testimony of the Augustan-era geographer Strabo's work "Geographica" VII.3.2 and 3.13, is disputed; opponents argue that Thracian was a distinct language from Dacian, either related or unrelated. (see Relationship with Thracian, below, for a detailed discussion of this issue).