Ante-Nicene Fathers, Vol VII:
Lactantius: Chap. X

Chap. X.

Diocletian, as being of a timorous disposition, was a searcher into futurity, and during his abode in the East he began to slay victims, that from their livers he might obtain a prognostic of events; and while he sacrificed, some attendants of his, who were Christians, stood by, and they put the immortal sign on their foreheads. At this the demons were chased away, and the holy rites interrupted. The soothsayers trembled, unable to investigate the wonted marks on the entrails of the victims. They frequently repeated the sacrifices, as if the former had been unpropitious; but the victims, slain from time to time, afforded no tokens for divination. At length Tages, the chief of the soothsayers, 1970 either from guess or from his own observation, said, “There are profane persons here, who obstruct the rites.” Then Diocletian, in furious passion, ordered not only all who were assisting at the holy ceremonies, but also p. 305 all who resided within the palace, to sacrifice, and, in case of their refusal, to be scourged. And further, by letters to the commanding officers, he enjoined that all soldiers should be forced to the like impiety, under pain of being dismissed the service. Thus far his rage proceeded; but at that season he did nothing more against the law and religion of God. After an interval of some time he went to winter in Bithynia; and presently Galerius Cæsar came thither, inflamed with furious resentment, and purposing to excite the inconsiderate old man to carry on that persecution which he had begun against the Christians. I have learned that the cause of his fury was as follows.  

Footnotes

[Nothing easier than for these to pretend such a difficulty, in order to incite the emperor to severities. They may have found it convenient to represent the sign of the cross as the source of their inability to give oracles.]