Actually, it's Gematria. While apocalypse may be quite symbolical and may had happened multiple times during the fall of empires, during the times of the Apostles, 666 was widely understood to mean "NRON QSR". Incidentally, in some translations, the number has been "translated" to 616. Incidentally, again, N=50, so 616 matches "NRO QSR" (one of them is a Greek, one of them is a Hebrew translit). So, all choices being possible, we may still be dealing with a fall of Rome, or fall of a new Rome. But anyway, I'd rather go with this interpretation, than an overinterpretation that pope's seat is actually "666".