I have a riddle. Can anyone solve it?

In my mind’s eyes, I see three circles joined in priceless, graceful harmony.

Two full as the moon, one hollow as a crown.

Two from the sea, five fathoms down.

One from the earth, deep under the ground.

The whole, a mark of high renown.

Tell me, what can it be?
AnonymousTell me, what can it be?
You first. The rest of us will check your guess.

The answer is a ring

Teachers: We supply a list of EFL job vacancies
Perseus: "Have courage, princess.What can it be?Three circles joined.Two moons and a crown...The answer is a ring!Two pearls in a circle of gold!The ring of the Lord of the Marsh.The pearl ring of Calibos. [Brings out Calibos' dismembered hand] Here, on the claw handof Calibos himself! [Throws Calibos' hand on the steps] The ring. A gift from his mother...[Looks up at statue]...the goddess Thetis.Is that the answer?Is that the answer? Tell me!...We fought in the swamp!I spared his life on one condition.That he renounce his curse.There will be no more bonfires.No more nightmares.Light has conquered darkness.You're free."