Caius, Presbyter of Rome (also known as Gaius) was a Christian author who lived and wrote towards the beginning of the 3rd century. Only fragments of his works are known, which are given in the collection entitled The Ante-Nicene Fathers. However, the Muratorian fragment, an early attempt to establish the canon of the New Testament, is often attributed to Caius and is included in that collection.
For the existing fragments from Caius' "Dialogue or Disputation Against Proclus," we are indebted to Eusebius, who included them in his Ecclesiastical History. In one of these fragments, Caius tells Proclus,
- "And I can show the trophies of the apostles. For if you choose to go to the Vatican or to the Ostian Road, you will find the trophies of those who founded this church." 
There is also another series of fragments Eusebius gives from a work called "Against the Heresy of Artemon," although the Ante-Nicene Fathers note says regarding the authorship only that it is "an anonymous work ascribed by some to Caius."
Caius was also one of the authors to whom the "Discourse to the Greeks concerning Hades" was ascribed at one time. (It was also attributed, much more famously, to Josephus and still appears in editions of the William Whiston translation of his collected works, but is now known to be excerpted from a work by Hippolytus of Rome.)
- "Catholic Encyclopedia entry on Caius". Archived from the original on 21 April 2012. Retrieved 14 July 2007.
- Salmond, S.D.F. ""Introductory Notice to Caius, Presbyter of Rome" from the Ante-Nicene Fathers, Vol. 5. (Ed. by Alexander Roberts and James Donaldson.)". Archived from the original on 2 November 2011. Retrieved 14 July 2007.
- ""Fragments of Caius. I.—From a Dialogue or Disputation Against Proclus" from the Ante-Nicene Fathers, Vol. 5". Archived from the original on 3 November 2011. Retrieved 14 July 2007.
- ""Fragments of Caius. II.—Against the Heresy of Artemon" from the Ante-Nicene Fathers, Vol. 5". Archived from the original on 2 November 2011. Retrieved 14 July 2007.
- Niese, Benedictus. "Encyclopaedia of Religion and Ethics entry on Josephus" (PDF). Retrieved 14 July 2007. (From the website of the Project on Ancient Cultural Engagement Archived 4 August 2007 at the Wayback Machine.)
- Goldberg, Gary. "Did Josephus write the "Discourse on Hades?" (from "Josephus Mail and FAQs")". Archived from the original on 13 July 2007. Retrieved 14 July 2007. (Part of the Flavius Josephus Home Page Archived 10 June 2007 at the Wayback Machine of G.J. Goldberg.)