The Great Fire of Rome in Juli 64 CE arose from the merchant shops around the Circus Maximus, where flammable goods had been stored. It went on for about ten days and destroyed about two thirds of the huge city.
„Neither through human effort nor through lavish gifts of the Princeps (Nero) nor through atonement offerings to the gods was the defamation made give way that the fire happened on command. Consequently, to get rid of this rumor, Nero fastened the culprits and inflicted the most exquisite tortures on a class which was hated for their aberrations and which the populace called Chrestiani. (…) …Which were sentenced not so much because of the crime of having laid fire to the city, rather because of their hatred against humankind.“ (Tacitus, „Annals“, 15,44; translation: mine. – Tacitus himself had been about seven years old at the time of the great fire.)
Some scholars opine that there were two types of Christian apocalyptics: The first kind expected God alone to effect the end of the world, while the second sort believed that this end had to be brought about by human action too. Consequently, these scholars think it is possible that Christian apocalyptics of the second type did in fact lay fire to the city. To me that assumption seems highly unlikely.
Ancient cities heavily burned, and actually completely burned down, statistically every thirty or forty years. The imagery of first century CE’s numerous Jewish apocalypses derives from precisely that eyewitnesses’ experience. „Fire falling from heaven“ is inspired by fire falling from the roofs, because the roofs burned „best“ and first. All light and heat that did not come directly from the sun came from some sort of open fire. The city of Rome at that time had a population of about half a million (Prof. Glenn R. Storey). The mere idea of something like fireguards was just about to be invented, let alone the idea of fire-proof building and urban-planning rules. From such conditions easily by accident a catastrophic scenery could arise that was by no means far-fetched to be associated with the end of the world.
In much-troubled first century CE, everybody vividly awaited the end of the world and was looking for signs of it everywhere all the time. This quest for heavenly signs was normally quite superstitious. But followers of the biblical religion, although they waited for signs just like everybody else, were very proud of not being superstitious like the pagans. Thus, for them it was particularly clear that when you are looking for signs, you are reasonably careful not to manufacture them yourself as misleading artifacts.
The Christians were different from a majority of Roman-Empire folks only in as far as firstly they regarded the end of the world not just as a possibility, but were sure about its imminence, and secondly judged it as something positive. Therefore, in 64-CE Rome, what happened may very well have been the following: By their apocalyptic tradition, Christians certainly were quite used to the idea that a great city fire was indeed a divine sign – but they were not particularly sad nor upset about it like all the others around them, because for them this sign meant that the Messiah was coming (back) whom they knew already as a radically good and lovely one. That „crazy“ attitude amidst all the flames, and may it have expressed however subtle and in mere baffling calm serenity, was unfavorably noticed by their horrified fellow citizens – and therefore decisively contributed to the suspicion against them which held them responsible for the disaster.
Otherwise it would be highly unlikely that already in the year 64 CE it was possible for any Non-Jew in the big city of Rome to differentiate a Christian from a Jew.