I'm reading Brent Winters' The Excellence of the Common Law right now, which relies heavily on the idea that the priesthood of Babylon fled to Pergamum when Babylon was conquered in 539 BC. The authority of this priesthood was then inherited by Rome when Attalus III willed the kingdom to Rome in the second century BC.
I'm trying to fact check this idea, and find some ancient source or other that backs it up, but I'm only able to find this idea repeated on conspiracy-theory type websites. Can anyone point me to a reputable source for this information, either confirming or debunking it?
Winters quotes William Burckhardt Barker's book Lares and Penates in establishing this idea, as well as Donald Grey Barnhouses' The Invisible War:
The king of Babylon [Nimrod] built a bridge across the Euphrates River and gave himself the title of the great bridge builder. The title was transferred, centuries later, to a king of Asia Minor [Attalus of Pergamos], was taken by the Caesars, and finally fell to the popes who boast in it today, Pontifex Maximus.