Achilles heel

To Achilles, one of the most popular heroes of Greek and Roman culture, protagonist of the Iliad.

By immersion in the waters of the Styx, one of the rivers of the underworld, Achilles became invulnerable. His mother held him by the heel while doing so, leaving that small part of his body vulnerable.

During the siege of Troy, he died from an arrow shot into his vulnerable heel from the walls of Troy with the help of Paris. Hence also 'Achilles tendon' : strong and thick tendon from the calf muscle to the heel.