Estimated Range of Dating: 130-200 A.D.
Chronological List of Early Christian Writings
Online Text for Epistle of Mathetes to Diognetus
English Translation by J. B. Lightfoot
Roberts-Donaldson English Translation
Online Resources for Epistle of Mathetes to Diognetus
Kirsopp Lake’s Introduction
Handbook of Patrology: The Letter to Diognetus
Geoff Trowbridge’s Introduction
Catholic Encyclopedia: Epistle to Diognetus
The Christian Life in the Epistle to Diognetus
Offline Resources for Epistle of Mathetes to Diognetus
Recommended Books for the Study of Early Christian Writings
Information on Epistle of Mathetes to Diognetus
Robert M. Grant describes the epistle of Mathetes to Diognetus (The Anchor Bible Dictionary, v. 2, p. 201):
A late 2d century apology addressed to a certain Diognetus who is otherwise unknown. Diognetus was a tutor of the emperor Marcus Aurelius, who admired him for his freedom from superstition and sound educational advice (Meditations 1.6), but he is not likely to be the recipient, or even the assumed recipient, of this apology from around A.D. 200. The work itself survived (with other writings ascribed to Justin) only in a 13th century manuscript, formerly at Strasbourg but burned during the invasion of 1870.
It is widely believed that the last two chapters were added at a later time. There are two schools as to its dating, one which favors a date approximately 130 CE and the other which favors a date approximately 200 CE or even later in the third century. I am not sure if there is evidence to resolve the question.
This work is an apology for the Christians, although the term Jesus or Christ is nowhere found in it, as the author seems to prefer the use of the term “the Word.”