I am rusty on the "full story", but Achilles was a prince of one of the Mycenaean kingdoms who was supposedly dunked in a sacred spring by his mum as an infant in order to give him invulnerability. She held him by his heel, and the heel was left "unprotected". He joined the other Mycenaeans in their assault on Troy. The event is shrouded in myth, but there is an historical base. Troy actually existed on the coast of Asia Minor. It was probably assaulted many times. Schliemann, the amateur archaeologist most known for its "discovery" places the war referred to in the mythology at around 1000 B.C. So do many others.

According to legend it was Achilles’ destiny to die in Troy despite his mother’s efforts to keep the prediction from coming true as well as the fact that without Achilles warrior skills the Greeks could not win despite Agamemnon’s desires. The story goes back 28 centuries. http://thelongestlistofthelongeststuffatthelongestdomainnameatlonglast.com/trivia9.html ......[EXCERPT from website for you].... ACHILLES -- THE LONGEST LIST OF THE LONGEST STUFF AT THE LONGEST DOMAIN NAME AT LONG LAST -- Achilles and Troy—The Legend, The Movie, The Truth The Hollywood trend of basing stories on legends, books, and historical events is not new and the fact that the movies are always different than what really happened is widely known and accepted. However, individuals who choose to simply view “Troy” as opposed to reading Homer’s The Iliad really miss out on some key events. Most importantly, the legend of Aquilles. Interestingly, the Troy War is one of the major surviving pieces of Greek mythology and with the 2004 movie of “Troy” many people became interested in what really happened. Basically, in the second year of the conflict King Agamemnon, ruler of the Greeks, and Achilles’ dispute began. The dispute began for many reasons, but basically because the Greeks could not win without Achilles and Achilles listened to his own warrior’s voice rather than Agamemnon’s directions. It is amazing Achilles fought for the Greeks when he was predestined to die in the engagement. According to legend it was Achilles’ destiny to die in Troy despite his mother’s efforts to keep the prediction from coming true as well as the fact that without Achilles warrior skills the Greeks could not win despite Agamemnon’s desires. When Achilles was a child his parents dressed him as a girl and sent him to live with a King. Also, Achilles mother tried to increase his protection and bathed him in the river to make him immortal, however the only vulnerable spot was his heel where she held him to immerse him in the immortal waters. As a result, Achilles’ only vulnerability was his heel.