ὅρκῳ πιστοῦν

From LSJ

ἔστιν δέ που ἡ μὲν ἐπὶ σώμασι γυμναστική, ἡ δ' ἐπὶ ψυχῇ μουσική → I think I am right in saying that we have physical exercise for the body and the arts for the soul

Source

Greek > English (Woodhouse)

bind by an oath