ACHILLES, TENDON OF. The large tendon inserted into the heel bone (calcaneus), at the back of the ankle, by means of which the calf muscles of the leg extend and invert the foot. These muscles sometimes become shortened, owing to overdevelopment, or sometimes to the continued use of high-heeled shoes, or they may be congenitally short. This defect sometimes leads to fallen arches and to pain in the foot so severe that lengthening the tendon by surgical means becomes necessary. This important tendon is named after Achilles, the great hero of the Trojan war and the central figure of Homer's Iliad. According to Greek legend, when Achilles was born, his mother dipped him in the river Styx. This bath made all parts of his body invulnerable except the heel by which she had held him, and it was in this heel that he later received a mortal wound.