You may think the capital of the Catholic Church's name is a religious one, but in actuality, the name was bestowed upon the land at the height of the Roman dynasty, which was not yet monotheistic.
This area to the west of the Roman Forum, Parthenon and Colosseum was nothing like the bustling civilization of Rome and instead a remote, marshy area called Ager Vaticanus. (Ager means "land" in Latin.)
In the 4th century, a basilica was constructed over the burial site of St. Peter the Apostle, who had been buried in a cemetery here in 64 A.D. To protect his grave and the basilica, Vatican City became home to the Catholic Church.
In Latin, Viaticum is the Eucharist given during Last Rites, but no one is is certain how the area originally received its Vatican name.