[1] Varro (1st century BC) connected it to a Deus Vaticanus or Vagitanus, a Roman deity thought to endow infants with the capacity for speech evidenced by their first wail (vagitus, the first syllable of which is pronounced [waː-] in Classical Latin).
Varro's rather complicated explanation relates this function to the tutelary deity of the place and to the advanced powers of speech possessed by a prophet (vates), as preserved by the later antiquarian Aulus Gellius: We have been told that the word Vatican is applied to the hill, and the deity who presides over it, from the vaticinia, or prophecies, which took place there by the power and inspiration of the god; but Marcus Varro, in his book on Divine Things, gives another reason for this name.
"As Aius," says he, "was called a deity, and an altar was built to his honour in the lowest part of the new road, because in that place a voice from heaven was heard, so this deity was called Vaticanus, because he presided over the principles of the human voice; for infants, as soon as they are born, make the sound which forms the first syllable in Vaticanus, and are therefore said vagire (to cry) which word expresses the noise which an infant first makes".
[2] St. Augustine, who was familiar with Varro's works on ancient Roman theology,[3] mentions this deity three times in The City of God.
Although secondary to this deity's main worship on the Palatine Hill, this temple gained such fame in the ancient world that both Lyon, in Gaul, and Mainz, in Germany called their own Magna Mater compounds "Vaticanum" in imitation.
However, the cathedral of the Bishop of Rome, the Pope, is not St. Peter's in the Vatican, but Basilica di San Giovanni in Laterano, which is extra-territorially linked, as indicated in the Lateran Pacts signed with the Italian state in February 1929, with the Holy See.