Matthew Poole and continuators on Revelation 17:11

11 And the beast that was, and is not, even he is the eighth , and is of the seven , and goeth into perdition .

This made the eighth succession of Governments in the Roman Empire.

This was of the seventh Head, for although this was the eighth Government in order as we have counted them; yet one of these, viz. the seventh, (which was that of true Christian Emperours) must not be counted as one of the seven Heads, which were all Idolatrous: So though this was the eighth Government, yet he was one of the seven Heads, i. e. Idolatrous Governments, and

to be destroyed as they were.