"Aristides also, a believer earnestly devoted to our religion, left, like Quadratus, an apology for the faith, addressed to Hadrian. His work, too, has been preserved even to the present day by a great many persons." (Hist. Eccl. 4.3.3)Jerome, in his "On Illustrious Men," also mentions Aristides and his Apology (ca. 393 CE).
"Aristides a most eloquent Athenian philosopher, and a disciple of Christ while yet retaining his philosopher's garb, presented a work to Hadrian at the same time that Quadratus presented his. The work contained a systematic statement of our doctrine, that is, an Apology for the Christians, which is still extant and is regarded by philologians as a monument to his genius." (De vir. 20)In this Apologetic work Aristides compares the Christian God with the Pagan God's. At one point, Aristides begins to point Hadrian to the Christian scriptures or writings in order to validate his arguments.
"Take, then, their writings, and read therein, and lo! you will find that I have not put forth these things on my own authority, nor spoken thus as their advocate; but since I read in their writings I was fully assured of these things as also of things which are to come. And for this reason I was constrained to declare the truth to such as care for it and seek the world to come. And to me there is no doubt but that the earth abides through the supplication of the Christians. But the rest of the nations err and cause error in wallowing before the elements of the world, since beyond these their mental vision will not pass. And they search about as if in darkness because they will not recognize the truth; and like drunken men they reel and jostle one another and fall." (Apol. 16)It appears that Aristides is stating that he was converted to Christianity after he accessed their writings and read them for himself. If we can trust his testimony here, I find it fascinating that Aristides was able to identify a collective body of recognizable Christian writings. In other words, there was at the time (ca. 117-138 CE), a collection of writings that were recognizable by a non-Christian outsider as their definitive supporting documents. In turn, Aristides expected Hadrian to be able to recognize these writings as well.
It is also interesting that these writings were even available to the outsider. Aristides does not mention how he obtained a copy, but it had to be either through a book seller, a library, a friend, or a Church. In the early decades of the second century, these early Christian writings were circulating to such a degree that a Philosopher in Athens could obtain copies and read them for himself.