Most theologians believe that mountains in the Bible represent kingdoms which can be proved by Daniel 2:35, "Then was the iron, the clay, the brass, the silver, and the gold, broken to pieces together, and became like the chaff of the summer threshingfloors; and the wind carried them away, that no place was found for them: and the stone that smote the image became a great mountain, and filled the whole earth."Jesus Christ, the stone that smote the image became a great mountain (great kingdom) and filled the whole earth. 

So what are the seven kingdoms (mountains) that the woman sitteth on in the verses below, and who were the seven kings or seven rulers over the seven kingdoms (mountains)? And who is the 8th king & what is the 8th kingdom?

Rev. 17:9-11, "And here is the mind which hath wisdom. The seven heads are seven mountains, on which the woman sitteth. And there are seven kings: five are fallen, and one is, and the other is not yet come; and when he cometh, he must continue a short space. And the beast that was, and is not, even he is the eighth, and is of the seven, and goeth into perdition." 

So the woman sitteth on seven mountains (seven kingdoms). There are seven kings: five are fallen, kings or rulers of Egypt, Assyria, Babylon, Media-Persia, Greece which are the first five kingdoms that once had control over Israel and had fallen. A Roman Caesar of the Roman Empire was the sixth when John wrote the book of Revelation, and the 7th was a Sultan over the Ottoman Empire. The 8th kingdom will be the kingdom of the Antichrist beast, and he is of the seven meaning he will come from one of the seven kingdoms that once controlled Israel with my guess being he will come from Iran (Media-Persia) which is the middle kingdom of the seven kingdoms that once controlled Israel just like Jesus Christ is the middle candlestick of the seven candlesticks (Menorah), and we also see Him standing in the midst of the seven candlesticks which are the seven churches in the book of Revelation.