M. TVLLI CICERONIS DE OFFICIIS LIBER TERTIVS
 Hinc ille Gyges inducitur a Platone, qui cum terra discessisset magnis quibusdam imbribus, descendit in illum hiatum aeneumque equum, ut ferunt fabulae, animadvertit, cuius in lateribus fores essent; quibus apertis corpus hominis mortui vidit magnitudine invisitata anulumque aureum in digito; quem ut detraxit, ipse induit (erat autem regius pastor), tum in concilium se pastorum recepit. Ibi cum palam eius anuli ad palmam converterat, a nullo videbatur, ipse autem omnia videbat; idem rursus videbatur, cum in locum anulum inverterat. Itaque hac oportunitate anuli usus reginae stuprum intulit eaque adiutrice regem dominum interemit, sustulit quos obstare arbitrabatur, nec in his eum facinoribus quisquam potuit videre. Sic repente anuli beneficio rex exortus est Lydiae. Hunc igitur ipsum anulum si habeat sapiens, nihil plus sibi licere putet peccare, quam si non haberet; honesta enim bonis viris, non occulta quaeruntur.
38 By way of illustrating this truth Plato introduces the familiar story of Gyges: Once upon a time the earth opened in consequence of heavy rains; Gyges went down into the chasm and saw, so the story goes, a horse of bronze; in its side was a door. On opening this door he saw the body of a dead man of enormous size with a gold ring upon his finger. He removed this and put it on his own hand and then repaired to an assembly of the shepherds, for he was a shepherd of the king. As often as he turned the bezel of the ring inwards toward the palm of his hand, he became invisible to everyone, while he himself saw everything; but as often as he turned it back to its proper position, he became visible again. And so, with the advantage which the ring gave him, he debauched the queen, and with her assistance he murdered his royal master and removed all those who he thought stood in his way, without anyone's being able to detect him in his crimes. Thus, by virtue of the ring, he shortly rose to be king of Lydia. Now, suppose a wise man had just such a ring, he would not imagine that he was free to do wrongly any more than if he did not have it; for good men aim to secure not secrecy but the right.
Source: Marcus Tullius Cicero. De Officiis. Translated by Walter Miller. Loeb Edition. Cambridge: Harvard University Press, 1913. http://www.stoics.com