It is no longer a secret that there are historical connections between the myths from everywhere in the world, indicating that every culture had strong influences on each other and their legends. A minor example of this can be seen in something as simple as a body armor – Ancient India’s Karna’s kawach (“armor”) has been compared with that of Ancient Greek’s Achilles’ Styx-coated body and with Ancient Irish warrior Ferdiad’s horny skin that could not be pierced.

Source: Magic Armor Can’t Save the Tragic Heroes: Duty & Doom for Karna, Ferdiad & Achilles | Ancient Origins Members Site