What does “Achilles’ heel” mean?

The phrase today

Call something an Achilles’ heel and you mean its one fatal flaw: a strong team’s slow defense, a brilliant student’s panic in exams, a fortress with a single unguarded gate. The image needs a body that is safe everywhere except one small place. That picture is not Homer’s. It is a Roman-era story that grew up around the hero of the Iliad.

Homer’s Achilles bleeds

In the Iliad, Achilles is the best of the Achaeans, as Homer calls him, but he can be hurt like anyone else. In book 21, beside the river Scamander, the Paeonian ally Asteropaeus, who could throw with either hand, hurls two spears at once. One sticks in Achilles’ shield. The other, in Samuel Butler’s translation, “grazed the elbow of Achilles’ right arm drawing dark blood” (21.166–168). What protects Homer’s hero is his speed, his skill and armor forged by the god Hephaestus. He knows he will die young, and the poem leans on that knowledge from start to finish.

Where the dipping comes from

The first surviving telling is the Achilleid of Statius, a Latin epic the poet left unfinished at his death around AD 96, some eight hundred years after Homer. Thetis, begging her grown son to hide from the war, reminds him what she did when he was born:

if at thy birth I fortified thee with the stern waters of Styx

Then she adds, “ay, would I had wholly!” The protection was incomplete. Statius does not spell out where the gap lay; later retellings put it at the heel she held him by.

Other ways to make a hero safe

Greek writers told a different story. Apollodorus, like Apollonius of Rhodes before him, says Thetis hid the baby in the fire by night to burn away what was mortal in him and rubbed him with ambrosia by day, until Peleus caught her at it and cried out, and she left for the sea (Library 3.13.6). A stranger late version, gathered in Frazer’s notes to Apollodorus, has Peleus pull the child from the fire when only an anklebone had burned and replace it with the anklebone of a swift giant named Damysus. Apollodorus also says the fatal arrow struck Achilles in the ankle (Epitome 5.3). The weak spot drifted toward the foot long before it settled on the heel.

From heel to tendon

Anatomy kept the name. In 1693 the Flemish anatomist Philip Verheyen used the Latin chorda Achillis, the cord of Achilles, for the thick tendon that joins the calf muscles to the heel bone, its first known appearance in print. Doctors still call it the Achilles tendon, which anatomy textbooks describe as the strongest in the body, and a torn one is a famous way for athletes to lose a season. How Achilles actually died, by Paris’s arrow at the Scaean gate, is told in how did Achilles die?, and the poem that never mentions the heel is the subject of what is the Iliad about?