My understanding was that heaven was a Biblical concept, and in the Bible, "hell" is simply the place you go when you die: "Sheol". The modern concepts appear to be borrowed from Greek mythology, where the modern "hell" is Tartarus, and the modern "heaven" is Elysian. (I guess the Biblical "Sheol" would be Asphodel?
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So the early Christian church didn't invent anything; they adapted something that already exists. That's very characteristic of the early church; it's uncharacteristic, from what I've seen, for the early church to make something up to attract the masses or scare them into believing. Scare tactics were used, for sure(possibly unintentionally), but not using tools they invented themselves. It's obvious to me that the church leaders at the time, at least most of them, believed every word they preached. (at least there's no reason, for me, to believe they were intentionally lying)