Katoptris

Katoptris (in Ancient Greek: καθρέπτς, meaning "looking glass") is Piper McLean's dagger and her primary weapon. It once belonged to Helen of Troy.

History
This knife was originally a wedding present to Helen of Troy from her husband Menelaus, and when looked upon, can show much more than the holder's reflection (as shown when Piper sees her father tied to a pole by the giant, Enceladus). Helen used the dagger as a mirror, which is why she named it Katoptris, meaning "mirror" or "looking glass." It was not used as a weapon when Helen was the owner.

Katoptris is a parazonium blade. It was mostly ceremonial, carried by high-ranking officers in the Greek armies. It showed that the wielder was a person of power and wealth, but it could be used well in a fight.

The Lost Hero
Piper finds and chooses it when Annabeth Chase takes her to the Armory. Annabeth tells her that the knife has probably never been in seen battle. Piper brings it on the quest, and uses it to kill multiple Gegeines while Jason is fighting Enceladus.

The Mark of Athena
Piper looks into Katoptris numerous times to catch glimpses of the future. She sees Jason riding Tempest against Percy. Her mother Aphrodite. The river god Achelous. Jason, Percy and herself drowning in a well. And lastly she sees the Romans planning an invasion of Camp Half-Blood.

Description
It is sheathed in worn black leather and is bound in bronze. Katoptris has a hilt made of polished wood with an 18 inch triangular blade made from Celestial bronze.

Owners

 * Helen of Troy - Former owner
 * Piper McLean - Current owner

Trivia

 * Katoptris is Greek for Mirror or Looking Glass. Annabeth speculates that Helen, its original owner used it only for this purpose and nothing else.
 * Although it is considered a weapon, it was never really used in battle by Helen.
 * Piper doesn't seem to use it until the fight to free her dad, until then she uses it as Helen did.
 * In The Mark of Athena, Katoptris is able to show Piper visions.