Revelation 6:7-8

The fourth seal....a pale horse, the rider's name death. It is also expounded of trials, afflictions, persecutions, and especially of plagues, over four parts of the earth, by which may be denoted the great power and extent of the Roman empire. In the Greek we read, over the fourth part of the earth; which some reconcile, by observing that the Roman empire had dominions under it in all the four parts of the world, east, west, north, and south; and that its dominions might be said to comprehend the fourth part of the world. (Witham) --- By the pale horse, and the rider, death, who sat upon it, followed by hell, are meant that dreadful mortality which ever attends famines, &c. He had power to kill with sword, with famine, &c. All these evils came upon the Roman people, and history has preserved the memory of them, to shew the truth of the prophecy here delivered by St. John. (Grotius; Calmet)