In recent years, I have read several books about possible ancient civilizations, some of them good, some not so good.  By ancient civilizations, I am talking about those that predate written history which goes back approximately five thousand years.  While these books don't all cover the areas and don't always come to the same conclusions, one thing is common to most of them: the idea that human civilization has grown through cycles.
    The generally accepted beliefs among archaeologist, historian, and many others is that the growth of human civilization has been a steady growth from very primitive to our current advanced (at lest in terms of technological accomplishments) state with only minor setbacks caused by wars and natural disasters.  But the growing evidence, as indicated in these many books, is that great civilizations existed in the distant path but were wiped out or reduced to very few survivors who had to learn all over again.  If you think that is impossible, ask your self what would happen with the young people of today if a major natural disaster such as an asteroid colliding with earth wiped out all of our civilization and left only a few scattered survivors.   Would they know how to find food with no supermarkets?  Would they be able to make their own clothes and homes?  I don't think most could do it.  So what would it be like a few generations later?  There would be only vague rumors of previous great cities and wonderful inventions that helped people do things, but few would believe those stories were anything more than fantasies.  And that is what probably happened in the distant past and can happen again.