In the 60s of the first century, Emperor Nero accused the Christians of Rome, probably unfairly, of starting the Great Fire of Rome. Richard Holland (
Nero: The Man Behind the Myth) points to the lack of an authentic and specific early Christian source for a mass persecution under Nero to support the view that this was not the start of a general persecution of the Christians, although it did result in the harrassment and expulsion of Christians from Rome.
Of course the Christians could be accused of atheism, a capital offence in pagan Rome, for not worshipping the Roman gods. However, most of the Roman emperors exercised restraint and leniency in this regard. In an exchange of letters between Pliny the Younger and the Emperor Trajan in about 112, Trajan said that Christians were not to be sought out for punishment, and if they came up in court they were to be given the opportunity of clearing themselves by formal denial, no matter how compromising their previous conduct may have been - so long as they also offer up the required prayers to the Roman Gods.
Emperor Decius, believed to be the first emperor to institute widespread, official persecution of Christians, condemned Christianity as a recent and criminal superstition. As Christianity continued to grow, the pagans were incensed at the Christians for so loudly presuming to accuse their countrymen of error, and for insisting that their ancestors were condemned to eternal misery for their paganism.
Michael Grant (
The Emperor Constantine) says that Christians incurred the displeasure of the pagan Roman government because they did not seem entirely loyal. The government liked to express the view that, by worshipping their own God instead of the pagan gods, the Christians were flouting the hallowed traditions of Rome. But what the emperors really meant was that these Christians could not be relied upon to do what the government required, preferring to accept the authority of their own bishops instead, and thus fostering disunity in the empire. Grant says that Emperors Diocletian and Galerius were alarmed by the powerful cohesion of the Christian communities, which they saw as a rival and therefore a threat to the cohesion of the empire as a whole.
Edward Gibbon (
The Decline and Fall of the Roman Empire) illustrates the apparent disloyalty of some Christians with the story of Marcellus, the centurion who threw away his arms and the ensigns of his office, and exclaimed with a loud voice that he would obey none but Jesus Christ the eternal King, and that he renounced forever the use of carnal weapons and the service of an idolatrous master. The soldiers, as soon as they recovered from their astonishment, secured the person of Marcellus. By his own confession, he was condemned and beheaded for the crime of desertion. Gibbon points out that in cases like this, the Roman response was not so much persecution but use of martial or even civil law in much the way nations would use them even today.
The Great Persecution of 303-311 was the most dramatic imperial response to the perceived threat posed by the Christian minority. Within fifteen days of the edict being published, the palace of Nicomedia, even the bedroom of Emperor Diocletian, were twice in flames. Both times the the flames were extinguished without any material damage, but the repetition of the fire was justly considered as an evident proof that it had not been the effect of chance or negligence. The suspicion naturally fell on the Christians.