In the Roman empire, Christians were persecuted under various emperors for their beliefs and for misunderstandings of their beliefs. One of the reasons that the Roman emperors persecuted Christians was syncretism: which is basically having a big mix of different gods that you believe in, both your original gods and the roman gods and whatever else you decide to worship. The Christians would not worship the gods of Rome or worship the emperor, and this would get them into trouble. Other reasons they were persecuted were misunderstandings, misrepresentations, and even outright lies about them. Some people said that the Christians practiced cannibalism; a misunderstanding of communion, and others thought that they had their new initiates kill babies. False reports like this were also a big cause of the persecution of the Christians.
We get a lot of information about how the Roman empire persecuted the Christians from a letter that was sent to the emperor Trajan from Pliny the younger, a roman official. In the letter, Pliny wanted to know from the emperor what he should judge concerning Christians, because he had never had a case where someone was accused of being a Christian. Trajan told him that he should keep doing what he was doing, which was not seeking them out for persecution, but waiting for them to be reported to him and then executing them if they didn’t worship the roman gods and do other things that Christians are not supposed to do.
But, sometimes it got a lot worse than this. One example is Nero, a roman emperor in the first century. Nero blamed the Christians for burning Rome and then proceed to kill many of them in various different ways. Some, like the apostle Paul, were beheaded. The apostle Peter was crucified. Others were used as torches to light his gardens, and others were thrown to wild beasts in the amphitheater or received other cruel punishments. Other emperors that persecuted Christians to a greater degree than the norm were Domitian, Decius, Diocletian, and others.