Invulnerability
Associated with this is invulnerability, variously bestowed or acquired. In the tradition of Achilles, he was immersed in the river Styx by his mother Thetis, but the immersion did not extend to his heel, in which he received his mortal wound from the arrow of Paris.
Jason was rendered invulnerable in his battle with the giants that sprang from the sowing of the Cadmean teeth by being anointed by Medæa with the Promethean unguent.
Siegfried, the horny, made himself similarly proof from injury by bathing in the dragon’s blood, but one spot on his back, where a linden leaf had stuck, escaped. Through this only vulnerable spot he met his death, being killed by Hagan the Dane while drinking in a pool.
This probably is a poetic allusion to early employment of defensive armour, in which the back, as compared to the front, would be unprotected.
Belief in Numbers
Certain numbers have at all times been invested with mystic significance, e.g., “Three” the “perfect” number, expressive of Beginning, Middle and End; also symbol of Deity. An earlier term of Trinity is Triad, and almost every mythology has a three-fold deity.
That of the ancient Greeks consisted of Zeus, Apollo and Aphrodite, the Egyptian being Osiris, Isis and Horus. The Romans believed the world to be under the rule of three gods—Jupiter (Heaven), Neptune (Ocean), and Pluto (Hades). The first has three thunderbolts—Neptune, the Trident, and Pluto, Cerberus, the triple-headed dog.
Three in number also were the Fates, Furies, Graces, Harpies and Sibylline Books. In the underworld the three judges of hell were Rhadamanthos, Minos and Æacos.