The Caduceus was the magic wand of the god Hermes. It was an olive staff twined with fillets, which were gradually converted to wings and serpents. Hermes, or Mercury, was the messenger of Jove. Among his numerous attributes, one of the most important was that of conducting disembodied spirits to the other world, and, on necessary occasions, of bringing them back. He was the guide of souls, and the restorer of the dead to life.

Thus, Horace, in addressing him, says:

Unspotted spirits you consign
To blissful seats and joys divine,
And powerful with your golden wand
The light unburied crowd command.
Vergil also alludes to this attribute of the magic wand
when he is describing the flight of
Mercury on his way to bear Jove's warning message to Aeneas:
His wand he takes ; with this pale ghost he calls
From Pluto's realms, or sends to Tartarus' shore.

And Statius, imitating this passage, makes the same allusion in his Thebaid (1, 314), thus translated by Lewis:

He grasps the wand which draws from hollow graves,
Or drives the trembling shades to Stygian waves ;
With magic power seals the watchful eye
In slumbers soft or causes sleep to fly.

The history of this Caduceus, or magic wand, will lead us to its symbolism. Mercury, who had invented the lyre, making it out of the shell of the tortoise, exchanged it with Apollo for the latter's magical wand. This wand was simply an olive branch around which were placed two fillets of ribbon. Afterward, when Mercury was in Arcadia, he encountered two serpents engaged in deadly combat. These he separated with his wand; hence the olive wand became the symbol of peace, and the two fillets were replaced by the two serpents, thus giving to the Caduceus its well-known form of a staff, around which two serpents are entwined.

Such is the legend; but we may readily see that in the olive, as the symbol of immortality, borne as the attribute of Mercury, the giver of life to the dead, we have a more ancient and profounder symbolism. The serpents, symbols also of immortality, are appropriately united with the olive wand. The legend also accounts for a later and secondary symbolism-that of peace.

The Caduceus then-the original meaning of which word is a herald's staff-as the attribute of a life-restoring God, is in its primary. meaning the symbol of immortality; so in Freemasonry the rod of the Senior Deacon, or the Master of Ceremonies, is but an analogue or representation of the Hermean Caduceus. This officer, as leading the aspirant through the forms of initiation into his new birth or Masonic regeneration, and teaching him in the solemn ceremonies of the Third Degree the lesson of eternal life, may well use the magic wand as a representation of it, which was the attribute of that ancient deity who brought the dead into life.

- Source: Mackey's Encyclopedia of Freemasonry