The beast that you saw was, and is not; and shall ascend out of the bottomless pit, and go into perdition: and they that dwell on the earth shall wonder, whose names were not written in the book of life from the foundation of the world, when they behold the beast that was, and is not, and yet is.
All Commentaries on Revelation 17:8 Go To Revelation 17
George Leo Haydock
AD 1849
The beast which thou sawest. This beast, which supports Babylon, may signify the power of the devil; which was, and is not, being much limited by the coming of Christ, but shall again exert itself under antichrist. The seven heads of this beast are seven mountains or empires, instruments of his tyranny; of which five were then fallen, as above, chap. xiii. ver. 1. The beast itself is said to be the eighth, and is of the seventh; because they all act under the devil, and by his instigation, so that his power is in them all, yet so as to make up, as it were, an eighth empire distinct from them all. (Challoner)