What is an Achilles' Heel? Definition and Mythology

A Powerful Hero Brought Down by a Fatal Flaw

Statue of Dying Achilles at Achilleion Palace & Museum in Corfu, Greece
Tim Graham / Getty Images News / Getty Images

The common phrase "Achilles' heel" refers to a surprising weakness or vulnerability in an otherwise strong or powerful person, a vulnerability that eventually leads to a downfall. What has become a cliche in the English language is one of several modern-day phrases that are left to us from ancient Greek mythology.

Achilles was said to be a heroic warrior, whose struggles over whether to fight in the Trojan War or not are described in detail in several books of Homer's poem ​"The Iliad." The overall myth of Achilles includes the attempt by his mother, the nymph Thetis, to make her son immortal. There are various versions of this story in the ancient Greek literature, including her putting him in fire or water or anointing him, but the one version that has struck the popular imagination is the one with the River Styx and the Achilles Heel.

Statius' Achilleid

The most popular version of Thetis' attempt to immortalize her son survives in its earliest written form in Statius' Achilleid 1.133-34, written in the first century AD. The nymph holds her son Achilles by his left ankle while she dips him in the River Styx, and the waters confer immortality on Achilles, but only on those surfaces that contact the water. Unfortunately, since Thetis dipped only once and she had to hold onto the baby, that spot, Achilles' heel, remains mortal. At the end of his life, when the arrow of Paris (possibly guided by Apollo) pierces Achilles' ankle, Achilles is mortally wounded.

Imperfect invulnerability is a common theme in world folklore. For example, there is Siegfried, the Germanic hero in the Nibelungenlied who was vulnerable only between his shoulder blades; the Ossetian warrior Soslan or Sosruko from the Nart Saga who is dipped by a blacksmith into alternating water and fire to turn him into metal but missed his legs; and the Celtic hero Diarmuid, who in the Irish Fenian Cycle was pierced by a venomous boar bristle through a wound to his unprotected sole.

Other Achilles Versions: Thetis's Intent

Scholars have identified many different versions of the Achilles Heel story, as is true for most ancient history myths. One element with lots of variety is what Thetis had in mind when she dipped her son in whatever she dipped him in.

  1. She wanted to find out if her son was mortal.
  2. She wanted to make her son immortal.
  3. She wanted to make her son invulnerable.

In the Aigimios (also spelled Aegimius, only a fragment of which still exists), Thetis--a nymph but the wife of a mortal--had many children, but she wanted to keep only the immortal ones, so she tested each of them by putting them in a pot of boiling water. They each died, but as she began to carry out the experiment on Achilles his father Peleus angrily intervened. Other versions of this differently crazy Thetis involve her unintentionally killing her children while attempting to make them immortal by burning off their mortal nature or simply deliberately killing her children because they are mortal and unworthy of her. These versions always have Achilles saved by his father at the last minute.

Another variant has Thetis trying to make Achilles immortal, not just invulnerable, and she plans to do that with a magical combination of fire and ambrosia. This is said to be one of her skills, but Peleus interrupts her and the interrupted magical procedure only changes his nature partially, making Achilles' skin invulnerable but himself mortal. 

Thetis's Method

  1. She put him in a pot of boiling water.
  2. She put him in a fire.
  3. She put him in a combination of fire and ambrosia.
  4. She put him in the River Styx.

The earliest version of Styx-dipping (and you'll need to blame or credit Burgess 1998 for this expression that will not leave my mind soon) is not found in the Greek literature until Statius' version in the first century CE. Burgess suggests it was a Hellenistic period addition to the Thetis story. Other scholars think the idea may have come from the Near East, recent religious ideas at the time having included baptism.

Burgess points out that dipping a child in the Styx to make it immortal or invulnerable echoes the earlier versions of Thetis dipping her children into boiling water or fire in an attempt to make them immortal. Styx dipping, which today sounds less painful than the other methods, was still dangerous: the Styx was the river of death, separating the lands of the living from the dead.

How the Vulnerability was Severed

  1. Achilles was in battle at Troy, and Paris shot him through the ankle then stabbed him in the chest.
  2. Achilles was in battle at Troy, and Paris shot him in the lower leg or thigh, then stabbed him in the chest.
  3. Achilles was in battle at Troy and Paris shot him in the ankle with a poisoned spear.
  4. Achilles was at the Temple of Apollo, and Paris, guided by Apollo, shot Achilles in the ankle which kills him.

There is considerable variation in the Greek literature about where Achilles' skin was perforated. A number of Greek and Etruscan ceramic pots show Achilles being stuck with an arrow in his thigh, lower leg, heel, ankle or foot; and in one, he reaches calmly down to pull the arrow out. Some say that Achilles wasn't actually killed by a shot to the ankle but rather was distracted by the injury and thus vulnerable to a second wound.

Chasing the Deeper Myth

It is possible, say some scholars, that in the original myth, Achilles was not imperfectly vulnerable because of being dipped in the Styx, but rather because he wore armor--perhaps the invulnerable armor that Patroclus borrowed before his death--and received an injury to his lower leg or foot that was not covered by the armor. Certainly, a wound cutting or damaging what is now known as the Achilles tendon would hinder any hero. In that manner, Achilles' greatest advantage--his swiftness and agility in the heat of battle—would have been taken away from him.

Later variations attempt to account for the super-human levels of heroic invulnerability in Achilles (or other mythic figures) and how they were brought down by something ignominious or trivial: a compelling story even today.


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Gill, N.S. "What is an Achilles' Heel? Definition and Mythology." ThoughtCo, Feb. 16, 2021, thoughtco.com/what-is-an-achilles-heel-116702. Gill, N.S. (2021, February 16). What is an Achilles' Heel? Definition and Mythology. Retrieved from https://www.thoughtco.com/what-is-an-achilles-heel-116702 Gill, N.S. "What is an Achilles' Heel? Definition and Mythology." ThoughtCo. https://www.thoughtco.com/what-is-an-achilles-heel-116702 (accessed March 23, 2023).