Revelation 17:9

"And here is the mind which hath wisdom. 

The seven heads are seven mountains, on which the woman sitteth."

Everybody just always assumes this verse means Rome.

Seven hills of Rome

Everybody forgets Constantinople has seven hills as well.

Seven hills of Istanbul

Constantinople was the capital city of the Roman/Byzantine 

(330–1204 and 1261–1453), 

and also of the brief Latin 

(1204–1261), 

and the later Ottoman empires

(1453–1923).

Lots of people believe the Antichrist will come from Rome.

Constantinople was the capital city of the Eastern Roman Empire.

Also?

Constantinople / Istanbul has a horn.

Golden Horn

Daniel 8:9

"And out of one of them came forth a little horn, 

which waxed exceeding great, 

toward the south, 

and toward the east, 

and toward the pleasant land.

The Antichrist will come from Turkey.

Turkey

Here's an alternate viewpoint.

The muslim antichrist theory