This brief monograph was first published in German in 1905, and the present Gracie translation was issued in 1981 on the basis of a 1963 German edition. Harnack's book remained a useful introduction and reference for its topic throughout the 20th century, with ample citations of ancient texts. The volume is made up of two related essays: "The Christian as Soldier" regarding the incorporation of military ideas in primitive Christian culture, and "The Christian Religion and the Military Profession" regarding the participation of early Christians in the Roman military and the conversion of soldiers to Christianity.

One of the interesting features of this treatment is some of the information about the development of Latin terminology in early Christianity. The term sacramentum, for instance, evidently denoted a military oath before it became used by Christians to signify a holy rite (53-5). The pivot of the usage was evidently the sense of a ceremony of induction (i.e. equally baptism into the church and the formalization of military enlistment). Meanwhile, the Latin word pagani originally meant civilians as opposed to soldiery, and it maintained that sense in the rhetoric of the Western church, while only in the East was it confused with the idea of rusticity (84). The use of pagani as a term for the uninitiate or profane may not even have been novel in Christianity.

Harnack explores the tension between pacifist Christian theology and militarized Christian rhetoric, noting that Hebrew scripture and apocalyptic literature were powerful influences supporting the latter. Ultimately, as Christianity became legitimized in the Empire, Christian culture developed a military conception of clergy to support a command hierarchy within the church, and a warrior framing for ascetics that would persist in the language of monasticism.

I was delighted by Harnack's recounting of an item of verbal liturgy prescribed to the Roman legions under Constantine, which he praises as "the root of all Christian army and battle songs." While he admits in a footnote, "The Christian nature of the song could be doubted," he quickly quashes such doubts--without ever convincing me that the song might not be addressed to the "Supreme, holy God" Sol Invictus rather than the Christian deity (102). This passage is consistent with Harnack's occasional credulity regarding the contents of Eusebius' Life of Constantine and other polemical Christian histories from late antiquity.

The Gracie translation eliminated Harnack's appendix supplying his quoted ancient texts in the original languages, although it retained an "Index of Passages" referencing citations within the monograph. The ample translator's introduction summarizes the reception of Harnack's book by other scholars, notably C. John Cadoux, Jean-Michel Hornus, and John Helgeland, along with a brief discussion of the theological motivations that drive the study of this question.