We don't know. From what I've read, we know a little bit about early theory, but don't know precisely what scales and intervals they were talking about.
We know quite a lot about Greek music theory (Thomas Mathiesen's Apollo's Lyre: Greek Music and Music Theory in Antiquity in the Middle Ages is the go-to source here: https://archive.org/details/mathiesen-1999-apollos-lyre/page...). Of course we don't have recordings, but we do have a solid understanding of the theory, and some very good guesses as to the scales and intervals.
