Achilles Heel

Contrary to popular belief, Homer's Iliad makes no mention of Achilles' invulnerability or his vulnerable heel. The story of Thetis dipping her infant son in the river Styx first appeared in Statius's Achilleid, written in the 1st century CE — centuries after Homer. The phrase entered English as a metaphor for a critical weakness around 1810, when poet Samuel Taylor Coleridge wrote of "that vulnerable heel of the British Achilles" in reference to Ireland, and was in common figurative use by 1840.