In regards to the destruction of the city Babylon the Great, Rev. 18:17-19 shows all the shipmasters, sailors and all those trading at sea with Babylon the Great, who are standing far off while weeping and wailing and saying how this great city had made them rich.

And Rev. 18:12-13 gives a list of merchandise that was sold to Babylon the Great that they won't be selling to her any more.  

Rev. 18:12-13, "The merchandise of gold, silver, and precious stones, and pearls, and fine linen, and purple, and silk, and scarlet, and all thyine wood, and all manner vessels of ivory, and all manner vessels of most precious wood, and of brass, and iron, and marble, And cinnamon, and odours and ointments, and frankincense, and wine, and oil, and fine flour, and wheat, and beasts, and sheep, and horses, and chariots, and slaves, and souls of men."

So the one thing on the above list that stands out is frankincense.  The city of Mecca in Saudi Arabia would have no need to buy and import frankincense by sea because frankincense comes from trees in South Arabia. 

However, if the Vatican City inside the city of Rome is Babylon the Great, she would have to import the frankincense which makes her a more likely candidate to be Babylon the Great than Mecca.  At one time the Vatican City was part of the city of Rome, and it is completely surrounded by the city of Rome. However, in 1929 it became an independent country.