Revelation 17:9-11 NIV

9 “This calls for a mind with wisdom. The seven heads are seven hills on which the woman sits.

References for Revelation 17:9

10 They are also seven kings. Five have fallen, one is, the other has not yet come; but when he does come, he must remain for only a little while.
11 The beast who once was, and now is not, is an eighth king. He belongs to the seven and is going to his destruction.

References for Revelation 17:11