The notes of the Ancient Greek musical system were organised into tetrachords, groups of four notes. Two tetrachords made an octave.
The central octave went:
{Hypate, Parhypate, Lichanos, Mese}, {Paramese, Trite, Paranete, Nete}
It gets rather more complicated than that; the paramese, for example, is an interstitial note, and the tetrachords keep going above and below the central octave. See Musical system of ancient Greece – Wikipedia