In perhaps his most elaborate pseudo-archeological charade, in the autumn of 1493, he undertook a well-publicized dig at Viterbo, during which marble statues of some of the most dramatic of the mythical figures associated with the city's legendarium appeared to be unearthed; they had all been "salted" in the site beforehand.

In this work, he published alleged writings and fragments of several pre-Christian Greek and Latin secular authors, destined to throw an entirely new light on ancient history.

One influential suggestion he made — in his commentary on the Breviarium de Temporibus of Pseudo-Philo — was that the genealogy of Jesus in the Gospel of Luke traced the lineage through the father of Mary.

[7] In the Breviarium de Temporibus, the Christ's grandfather Eli according to Luke was identified with Eliachim, an alleged variant of St Joachim, the Virgin Mary's father according to the apocryphal Protoevangelium of James.

His Auctores vetustissimi printed at Rome, 1498, was an anthology of seventeen purportedly classical texts, all of which he had written himself, with which he embarks in the gigantic attempt to write a universal history of the post-diluvian West civilization, where the Etruscan people and the town of Viterbo/Etruria, custodian of the original knowledge of divine nature, takes on the leading role in the march of Man towards the future.

Analyzing the works of Diodorus Siculus, Annius supposed Isis and Osiris established new colonies in the Mediterranean Sea, the latter founding Viterbo, so as to derive a divine and Egyptian ancestry for the family of the ongoing Pope Alexander III, brother of Ranuccio.

In 1565–66, the humanist Girolamo Mei was engaged in a historiographical argument with Vincenzo Borghini, who presented a claim, for the occasion of the marriage of Francesco I de' Medici and Joanna of Austria, that Florence was founded by Augustus.

The volume Annio da Viterbo, Documenti e ricerche (Rome: Multigrafica Editrice for CNR, 1981) presents an unpublished work written by Annius: the Viterbiae historiae epitoma in the critical text edited by Giovanni Baffioni.