This article is focused around chronological view on persecution of first Christians in Roman Empire and possible causes why were the early Christians persecuted. Persecution of Christians in Roman Empire is without a doubt one of the most important event in history of this religion. Today, Christianity is the largest religion in the world, but in its humble beginning it was considered like underground movement. Central figure of this religion, Jesus Christ was sent on Earth to redeem people and by doing so He established new religion which occurred from Jewish religion. Because of this Roman’s saw first Christians as Jewish sect. Because of its rapid expansion Christianity will become state religion of Roman Empire. Persecution of Christians had three phases, and first one began when emperor Nero falsely blamed them for big fire in Rome, and started to persecute them. Many emperors after Nero persecuted Christians but those persecutions were mostly local. First emperor that decided to persecute them throughout all the empire was Emperor Decius. He demanded from all the people in the empire to sacrifice animal and this of course for the Christians was not acceptable. First laws against the Christians were issued by emperor Valerian and one of the worst persecutions for the Christians happened when Diocletian was emperor. Still, Christianity was spreading really fast across the Empire. After decades of fear and persecutions finally emperor Constantine the Great issued Edict of Milan in 313. A.D. when Christianity become allowed religion in the Roman Empire.