During the first three Centuries Christians in the Roman Empire were subjected again and again to harassment and persecution by the government. This is, at a first glance, rather surprising, for the Christian faith is not promoting crime or anarchy, but explicitly respects civil, even pagan, governments. Furthermore, the Romans were usually tolerant in religious matters and remarkably good at integrating foreign cultures.
So what had gone wrong in the case of Christianity?
For the people in antiquity, atheism was not an option (except for some esoteric philosophers): For them, the world was ruled by gods and inhabited by spirits and demons. Demons were responsible for disasters and illness. The latter view can be found even in the bible: When Jesus heals sick people, this is reported as “driving out demons”. Gods and demons could be influenced with prayers and sacrifices.
Consequently, superstitious Roman masters forbade their slaves to pray to their own gods—lest they invoke the wrath of their deities on them. A Christian slave refusing to venerate his masters' gods and secretly attending mass was eventually considered a threat.
Another important aspect of antique thinking is the association of deities with towns or states. The Romans believed that the Roman gods governed the world and protected the Roman Empire, but not on an exclusive base: The deities of other nations were assumed to exist, too.
Venerating the gods of an enemy, or even refusing to venerate the Roman gods could be regarded as high treason! However, this was usually not a problem: The Romans matched the foreign gods to their own ones (e.g., the Greek Zeus or the Germanic Thor to their main god Jupiter) or assigned them niches in the Roman olymp. But this “inculturation” of gods was not possible for the monotheistic religions, Judaism and Christianity. It is therefore not surprising that these religions were regarded with deep distrust.
Mere distrust, however, quickly developed into persecution after some disasters—epidemics, town fires, etc.—for which the Christians were blamed.
Fortunately, not all Roman Emperors promoted persecutions. Vespasianus, for instance, forbade the persecution of Christians, because the Roman gods should be capable of punishing them, if they were interested. Other emperors were not as wise. Diocletianus required ritual sacrifices to Roman gods as a proof of loyalty; refusing to sacrifice was considered high treason.
E. Long: “Diana or Christ?” (1888).
The girl is supposed to take frankincense from the box offered to her, and to sacrifice it to the goddess Diana (represented by a sculpture, a copy of the multi-breasted “Diana of Ephesus”, one of the seven antique wonders of the world. Evidently she has hesitated too long: The faces of the Roman official on the left side and the bearded priest indicate trouble …
But all such efforts to keep the old Latin town religion alive were doomed to fail. At the begin of the 4th Century, the Roman gods were no longer taken serious, and Emperor Constantin the Great installed Christianity as the official religion of the Empire.