Creative illustration. Magic. Mercury or Mercurius l is a major Roman god, being one of the Dii Consentes within the ancient Roman pantheon. He is the patron god of financial gain, commerce, eloquence, poetry), messages and communication, divination, travelers, boundaries, luck, trickery and thieves; he is also the guide of souls to the underworld. Mercury's swift flights from place to place. He is often depicted holding the caduceus in his left hand.