After Adrian, the churches had peace under the rule of Antoninus Pius. Then the fifth persecution began under Aurelius, the son of Antoninus. And then, for the first time, martyrdoms were seen taking place in Gaul, for the religion of God had been accepted somewhat late beyond the Alps. Then the sixth persecution of the Christians took place under the emperor Severus. At this time Leonida, the father of Origen, poured forth his sacred blood in martyrdom. Then, during an interval of thirty-eight years, the Christians enjoyed peace, except that at the middle of that time Maximinus persecuted the clerics of some churches.
Before long, under Decius as emperor, the seventh bloody persecution broke out against the Christians. Next, Valerian proved himself the eighth enemy of the saints. After him, with an interval of about fifty years, there arose, under the emperors Diocletian and Maximian, a most bitter persecution which, for ten continuous years, wasted the people of God. At this period, almost the whole world was stained with the sacred blood of the martyrs. In fact, they vied with each other in rushing upon these glorious struggles, and martyrdom by glorious deaths was then much more keenly sought after than bishoprics are now attempted to be got by wicked ambition.
Never more than at that time was the world exhausted by wars, nor did we ever achieve victory with a greater triumph than when we showed that we could not be conquered by the slaughters of ten long years. There survive also accounts of the sufferings of the martyrs at that time which were committed to writing; but I do not think it suitable to subjoin these lest I should exceed the limits prescribed to this work.
Source: Sacred History (New Advent)