A “great city” is a place where thousands of people live. This speaks not only to where the witnesses testified but more specifically to how many rejected their testimony. This “great city” is not one specific city (Jerusalem, Babylon, or some other city) no more than the two witnesses were two specific people, but represents any place of any time where the prophetic witness of the church has been rejected.
8 and their dead bodies will lie in the street of the great city that symbolically is called Sodom and Egypt, where their Lord was crucified.