[2] Returning to Italy, he made an attempt to teach in Genoa but was driven again to France, where he tried to clear himself of suspicion by publishing a book against atheism: Amphitheatrum Aeternae Providentiae Divino-Magicum (1615).

His father was Giovan Battista Vanini, a businessman from Tresana in Tuscany, while his mother was the daughter of a man named Lopez de Noguera, a customs contractor of the Spanish royal family's lands in Bari, Terra d'Otranto, Capitanata, and Basilicata.

A document dated August 1612, discovered in the Vatican Secret Archives, describes Vanini as of Apulia, which is consistent with the native land he mentions in his own works.

[3] Afterwards, he remained in the Naples area for two years, apparently living as a friar,[3] or alternatively he returned to Lecce and studied the new Renaissance sciences, chiefly medicine and astronomy.

By now, he had assimilated much knowledge and "speaks very good Latin and with great ease, is tall and a bit thin, has brown hair, an aquiline nose, lively eyes and a pleasant and ingenious physiognomy".

[3] Consequently, the Prior General of his order, Enrico Silvio, commanded him to return to Naples, where he would have been disciplined, probably severely, but instead Vanini sought refuge with the English ambassador to Venice in 1612.

They passed through Bologna, Milan, the Swiss canton of Graubünden, and descended via the Rhine, through Germany and the Netherlands, to the North Sea coast and the English Channel, finally reaching London and the Lambeth residence of the Archbishop of Canterbury.

[3] Around the start of 1614, Vanini visited the Universities of Cambridge and Oxford and confided to some acquaintances his imminent flight from England, so in January, he and Genocchi were arrested on the orders of the Archbishop of Canterbury, George Abbot.

He then journeyed to Italy, going first to Rome, where he had to face the difficult final stages of the process in the court of the Inquisition, then to Genoa for a few months, where he found his friend Genocchi and taught philosophy to children of Scipio Doria for a time.

The De Admirandis was a summa, lively and brilliant, of the new knowledge, and became a kind of "manifesto" for these cultural free spirits, giving Vanini a chance to stay safe in circles close to the French court.

However, a few days after the publication of the work, the two theologians at the Sorbonne who had expressed their approval were presented to the Faculty of Theology in formal session and the outcome was a de facto ban on the movement of the text.

Fearing that a court case would be started against him in Paris, he fled and went into hiding at Redon Abbey in Brittany, where Abbott Arthur d'Épinay de Saint-Luc acted as his protector.

But other factors gave cause for concern: in April 1617 Concino Concini, favorite of Marie de' Medici, was killed in Paris, giving rise to a wave of hostility to Italian residents at court.

In the following months, a mysterious Italian, with a strange name (Pompeo Uciglio[3]) and in possession of great knowledge but an uncertain past, appeared in some cities of Guyenne, then the Languedoc and finally Toulouse.

Duke Henri II de Montmorency, protector of esprits forts of the time, was the governor of this region and seemed to grant protection to the fugitive, who still continued to keep carefully hidden.

Amphitheatrum Aeternae Providentiae divino-magicum, christiano-physicum, necnon astrologo-catholicum adversus veteres philosophos, atheos, epicureos, peripateticos et stoicos (possible translation: "Amphitheatre of Eternal Providence – Religio-magical, Christian-physical and Astrologico-Catholic – against the Ancient Philosophers, Atheists, Epicureans, Peripatetics and Stoics"), published in Lyon in 1615, consists of 50 exercises, which aim to demonstrate the existence of God, to define His essence, to describe His providence and to examine or refute the opinions of Pythagoras, Protagoras, Cicero, Boethius, Thomas Aquinas, the Epicureans, Aristotle, Averroes, Gerolamo Cardano, the Peripatetics, the Stoics, etc.

De Admirandis Naturae Reginae Deaeque Mortalium Arcanis (possible translation: "On the Marvelous Secrets of Nature, the Queen and Goddess of Mortals"), printed in Paris in 1616 by publisher Adrien Périer, is divided into four books: These contain a total of 60 dialogues (but really only 59, as dialogue XXXV is absent), which take place between the author, in the role of disseminator of knowledge, and an imaginary Alessandro, who urges his interlocutor to list and explain the mysteries of nature found around and within man.

In a mixture of reinterpretation of ancient knowledge and the dissemination of new scientific and religious theories, the protagonist discusses: the material, figure, colour, form, energy and eternity of heaven; the motion and the central pole of the heavens; the sun, the moon, the stars; fire; comets and rainbows; lightning, snow and rain; the motion and rest of projectiles in the air; the impulsion of mortars and crossbows; winds and breezes; corrupt airs; the element of water; the birth of the rivers; the rising of the Nile; the extent and saltiness of the sea; the roar and the motion of the water; the motion of projectiles; the creation of islands and mountains, as well as the cause of earthquakes; the genesis, root and colour of the gems, as well as spots of stones; life, food, and the death of the stones; the strength of the magnet to attract iron and its direction toward the Earth's poles; plants; the explanation to be given to certain phenomena of everyday life; semen; the reproduction, nature, respiration and nutrition of fish; the reproduction of birds; the reproduction of bees; the first generation of man; stains contracted by children in the womb; the generation of male and female; parts of monsters; the faces of children covered by larvae; the growth of man; the length of human life; sight; hearing; smell; taste; touch and tickle; the affections of man; God; appearances in the air; oracles; the Sibyls; the possessed; sacred images of the pagans; augurs; the miraculous healing of diseases reported in pagan times; the resurrection of the dead; witchcraft; dreams.

"God acts on sublunary beings [humans] using the sky as a tool": hence the natural and rational explanation of the allegedly supernatural phenomena, since even astrology was considered a science.

Since Vanini in his works obscured his ideas, a typical ploy at the time to avoid serious conflicts with the religious and political authorities, the interpretation of his thought is difficult.

In 1623 two works appeared that started the myth of Vanini the atheist: La doctrine curieuse des beaux esprits de ce temps ... of Jesuit François Garasse, and Quaestiones celeberrimae in Genesim cum accurata explicatione ..., of Father Marin Mersenne.

In that same year the name of Vanini was again brought to the attention of French culture during the sensational trial of the poet Théophile de Viau, whose outlook had striking similarities with Vaninian thought.