One of the oldest of Roman Gods, Vediovis (Vejovis) is thought to be the first God to be born. Who Vediovis is became obscure through the years. He is depicted as a young man holding arrows or lightening and accompanied by a goat. Every spring in Rome, goats were sacrificed ritu humano (in the manner of human sacrifice) to Vediovis to avert plagues. This indicates that He is a God of the Underworld who could prevent or bring plagues.
Vediovis is the opposite of Jupiter. While Jupiter defended Rome, Vediovis was asked to attack the enemy cities. According to Macrobius, the Roman generals would pray to Dis Pater (God of the Underworld Treasures), Vediovis and the Manes (The Dead) to throw the enemy city into panic and terror. Therefore, Jupiter is the God of Defense and Vediovis is that of Offense.
In 200 BCE, Lucius Furius Purpureo vowed a temple to Vediovis for his help against the Gauls. Tribes in Cisalpine Gaul, spurred by the Carthaginian general Hamilcar, attacked and sacked Roman towns. Purpureo ended the siege of Cremona (and the attacks) with a brilliant victory. The Praetor of Cisalpine Gaul credited his win to Vediovis.
Note: Vediovis is not the Roman counterpart of Aesculapius, the God of Medicine, as popularly believed.