21st if May is one of the festivals of this very obscure Roman deity, who was worshipped on at least three dates in the Roman calendar.
On the 21st of May it was said that female goat was sacrificed to him, to avert plagues, and the phrase used to describe this means something like 'in the manner of a human sacrifice'.
Vejovis is so obscure that even the Romans were not sure what he was the god of. He is depicted on coins and in statuary as a naked, beardless, youth, carrying arrows and accompanied by a goat. Because of the construction of his name ve-jovis he is interpreted both as a youthful Jove and as Jove of the Underworld - Ve-jovis could mean the anti-Jove or the darker, chthonic Jove.
It is also thought that he may be a pre-Roman or Etruscan deity who has been carried into the classical panthaeon, but whose original function has been forgotten.
Because his function was not clear, and yet he was obviously important enough to have his own temple sited in a valley between two other hilltop groves (which was discovered and excavated in the 1930's) and three feast days, he was assigned functions based on his appearance as youthful Jove and his attributes such as the arrows, which are also associated with Apollo (the arrows of Apollo are the sun's rays, in the same way as the arrows of Artemis are moon beams). Thus in later Roman times he was worshipped as a god of healing (as was Apollo), and he was believed to have been an escapee from Hades, the Underworld kingdom of Pluto, who made it to heaven and sought refuge amongst the gods there. As an escapee, he became the god of persecuted people, those escaping injustice or those suffering because of the prejudices of the majority (sounds like a good deity for Witches!)
However, there is another interpretation which could be made of Vejovis, which looks further back than classical Roman or Greek mythology (which much of the Roman religion is based upon), to the time when it was not the male god who dominated heaven.
No religion springs fully formed into being. All religions are based on and in those which preceded them.
Islam and Christianity are based on the Jewish religion, and the Jewish religion is based on and incorporates elements from still older religions. Older religions where the Goddess was the supreme deity.
And one of the oldest stories tells of the love of the Goddess for a mortal who is the youthful tender of flocks and herds, and, for one reason or another, the youth dies and his spirit is drawn down into the Underworld. The Goddess follows him into the Underworld and through sacrifice, magic and bargaining she enters a contract with the powers of the Underworld that her lover will be allowed to live on the Earth again, but only for a certain length of time and then he will be obliged to return to the Underworld - thus explaining the apparent 'death' of the Earth in Winter and its 're-birth' in Spring.
Now let us look at Vejovis in light of this myth: Here we have a youthful god, associated both with flocks and with the Underworld. He is an archer (as was Attis, another lover of a Goddess), his arrows used to protect his flock of goats. And on the 21st of May to ensure that the flocks will grow and flourish, one of their number must be offered in place of Vejovis. This sacrificial goat fulfills several functions: it is an offering; it dies in place of the God allowing him to remain in the upper world; and it is the 'scapegoat', it dies so that plagues and suffering will not come to humanity, and it carries the sins of humanity to be buried in the Underworld.
So perhaps Vejovis should not be seen as the 'anti-Jove' but as the 'proto-Jove', the god he was before he became Jove, Lord of Heaven, King of the Gods.
Before Jove was all those things, he was Vejovis, a youthful god of flocks, who loved a Goddess, died and was reborn each year.