“Fear none of those things which you shall suffer. Behold, the devil shall cast some of you into prison, that you may be tested, and you will have tribulation ten days. Be faithful to death, and I will give you a crown of life” (Revelation 2:10).
As the Christian church was growing rapidly among the poor and disenfranchised, the Roman government began to be alarmed. Here was an organization which taught the poor that all were equal, which taught the slaves that all were free, which taught that “we ought to obey God rather than men” (Acts 5:29). The church also had by this time a highly organized hierarchy of bishops, elders and deacons. This was a period of disarray and decline for the Roman empire, with 60 different men proclaimed emperor between AD 235 and 284. In that year Gaius Diocletian was proclaimed emperor and he immediately began to consolidate his power and to try to bring control and stability to the empire. His attention was soon fixed on the Christians as the cause of the evils of the time because they offended the traditional Roman gods and refused to worship the emperor. In AD 303 Diocletian forbade Christian worship, ushering in the “Great Persecution” the last and most severe persecution of Christians in the Roman Empire. The reign of terror continued for 10 years until 313 (the “ten days” of tribulation). By that time Constantine the Great had become emperor. He realized that political control of the church would be more effective than attempts to eradicate it, so he granted Christians freedom of worship.
Painful though these persecutions were, they kept the Church relatively free of hypocrites. Jesus did not condemn the church of Smyrna, even though the Nicolaitan and synagogue-of-Satan heresies were beginning to show their presence; He simply encouraged the church in the face of persecution to “be faithful unto death.” Death is often considered to be the ultimate enemy, but Jesus had told his disciples, “do not be afraid of those who kill the body, and after that have no more that they can do” (Luke 12:4). Now He repeats that promise, and reveals the rich reward to those who make the ultimate sacrifice: “He who overcomes shall not be hurt by the second death…and I will give you the crown of life. (Revelation 2:11)”
 This is an example of the “day for a year” principle of prophecy. See Appendix 5 for a full explanation.
 Wikipedia contributors, "Diocletianic Persecution," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/w/index.php?title=Diocletianic Persecution&oldid=61328269 (acessed June 25, 2014).