Origins of End of Days prophecy?

l can remember reading where the story of End Days and Rapture and all the cool stuff Christians are waiting for - wasn’t actually written about - until the middle ages, when some cleric, perhaps after some moldy Rye bread - wrote it all down…
was it God’s hand . . . or could it have been Ergot doing the talking?
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OK the ergot is pure fanciful speculation on my part, although seems to me the dude had to have been on something pretty powerful.
But, the other part about the origins of the ginned up End of Days interpretation being created in the middle ages - that I’m not making up. However, I’m having a hard time finding something solid on it, and don’t have much free time so I’m seeking a little help.
Can anyone out there help me with some info?

Or even later… like the early 1800…
? ? ?

This article has a lot of Christian scholar jargon, but if you can wade through it, perhaps you can find some of what you are looking for. :
http://www.raptureforums.com/Rapture/mythsoriginspretribrapture1.cfm

Re: moldy bread and psychogenic effects having an impact on interpretations of the book of Revelations, I don’t think one would need a psychogenic substance to come up with a variety of interpretations out of that exceedingly wierd book. Throw in a touch of religious obsessiveness and rigid adherence and exposure to religious ritual, and you could have psychogenic effect enough, if that were needed.

Or even later... like the early 1800... ? ? ?
Citizen, I would look into religion in the US in the early 1800's. The transformation of churches into evangelical movements. If I'm not mistaken these ideas coincided with the philosophy of salvation. The idea that people are here on Earth to only do gods work. Look up "Millennial" or the "millennium". Also "post-millennialism" More search words would be the origin of "chiliasm". Of course these all have roots in older European and Middle Eastern religions but, the 19th century was a great awakening for these ideas and many were very much part and parcel to the forming of the American "thing"(sorry best word I could find.) These millennial philosophies were perfect for the US at the perfect time and place. A very unique juxtaposition in time and place. The First and Second Great Awakenings...another place to poke around for info. The things that came to America were this new ideology. That's why so many came to the US. Beforehand, back in Europe, religion and god was not something that average people could be enfranchised with for the most part. This new ideology came to the US and suddenly everyone could get on board. Common people suddenly felt part of a Great Spirituality. They felt they had stakes in the whole show. This, people generally never had before. And repeating myself...The US was perfect for it. Perfect time, Perfect place..Lot's of room, and few catholics. In a nutshell. That's oversimplified. By emphasizing a millennial ideology evangelicals got everyone on board for making the US a heaven on Earth for the coming of christ. It was powerful. It had many great advantages....much of what we would view as liberal today. Obviously it has transmogrified into something very heinous today.

I know my reply was a little off base, unless your looking for the reasons for the prevalence of this in the US.
The origins of millennialism go way back. Obviously before christianity and the book of revelations.