From the year A.D. 173 and onwards evidence of Christians in the rank and controversies over military service increased. Tertullian, in Apology written in A.D. 197, refuted the charge of misanthropy which was leveled against Christians by pointing to their presence in the palace, the Senate, the forum, and the army. His stern rebuke in the De Corona (A.D. 211) of voluntary enlistment is a witness to the practice which he condemned along with Christian rejection of military service. The number of Christians in the army is considered to have increase during the latter part of the third century, because even before the great persecution of A.D. 303-4, Galerius sought to weed Christians out of his forces. When persecution broke out a number of Christians in the armies of Constantine and Lincinius in their campaign against Maxentius and Maximus Daza. Licinius himself prescribed for his soldiers a form of prayer, which was monotheistic, if not overtly Christian. The whole matter began to take a decisive turn with the reign of Constantine. We hear of no more military martyrdoms. Strangely enough, laws were enacted prescribing severe ecclesiastical penalties for desertion in time of peace. In A.D. 416 Theodsius II was to exclude pagan from the army of the empire. and two centuries later, it was only with difficulty that the emperor Phocas was dissuaded from his opinion that all his soldiers who met a heroic death in battle should be honored as martyrs. From this it was but a step to the idea of the crusade, a holy war on behalf of the Christian church.
(272.3)