“Bottomless pit” is one word in the Greek of the New Testament and is literally the “abyss,” which means “bottomless, unbounded, the pit, or the immeasurable depth.” Roman mythology featured a similar place called Orcus, a very deep gulf or chasm in the lowest parts of the earth used as the common receptacle of the dead and, especially, as the abode of demons. The bottomless pit of Revelation 9:1-12 holds a unique type of demon. It is also the home of the beast who makes war against the two witnesses (Revelation 11:7-8.). At the beginning of the millennial kingdom, the bottomless pit is the place where Satan is bound (Revelation 20:1-3). At the end of the thousand years, Satan is released and promptly leads an unsuccessful revolt against God (Revelation 20:7-10).

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Comment: There is something unsettling about the word 'bottomless'. It signifies I think, a fall that is continuous - forever. If some place is bottomless you will never hit the ground.