See Tillemont, Memones Ecclesiastiques, tom.v.part ii.p.

320.] His fears were soon alarmed by the view of a danger from which he very narrowly escaped.

Within fifteen days the palace of Nicomedia, and even the bed-chamber of Diocletian, were twice in flames; and though both times they were extinguished without any material damage, the singular repetition of the fire was justly considered as an evident proof that it had not been the effect of chance or negligence.

The suspicion naturally fell on the Christians; and it was suggested, with some degree of probability, that those desperate fanatics, provoked by their present sufferings, and apprehensive of impending calamities, had entered into a conspiracy with their faithful brethren, the eunuchs of the palace, against the lives of two emperors, whom they detested as the irreconcilable enemies of the church of God.
Jealousy and resentment prevailed in every breast, but especially in that of Diocletian.

A great number of persons, distinguished either by the offices which they had filled, or by the favor which they had enjoyed, were thrown into prison.