1911 Encyclopædia Britannica/Caduceus
CADUCEUS (the Lat. adaptation of the Doric Gr. καρύκειον, Attic κηρύκειον, a herald's wand), the staff used by the messengers of the gods, and especially by Hermes as conductor of the souls of the dead to the world below. The caduceus of Hermes, which was given him by Apollo in exchange for the lyre, was a magic wand which exercised influence over the living and the dead, bestowed wealth and prosperity and turned everything it touched into gold. In its oldest form it was a rod ending in two prongs twined into a knot (probably an olive branch with two shoots, adorned with ribbons or garlands), for which, later, two serpents, with heads meeting at the top, were substituted. The mythologists explained this by the story of Hermes finding two serpents thus knotted together while fighting; he separated them with his wand, which, crowned by the serpents, became the symbol of the settlement of quarrels (Thucydides i. 53; Macrobius, Sat. i. 19; Hyginus, Poet. Astron. ii. 7). A pair of wings was sometimes attached to the top of the staff, in token of the speed of Hermes as a messenger. In historical times the caduceus was the attribute of Hermes as the god of commerce and peace, and among the Greeks it was the distinctive mark of heralds and ambassadors, whose persons it rendered inviolable. The caduceus itself was not used by the Romans, but the derivative caduceator occurs in the sense of a peace commissioner.
See L. Preller, "Der Hermesstab" in Philologus, i. (1846); O.A. Hoffmann, Hermes und Kerykeion (1890), who argues that Hermes is a male lunar divinity and his staff the special attribute of Aphrodite-Astarte.