During the millennial reign, Christ will set up His throne on earth in the city of Jerusalem. From there He will rule the earth with the help and administration of the Christians who were raptured and the Jews who overcame the tribulation, not to mention the angels. This city later in the millennium becomes the focal point of Satan at his release and he wages war against it with volunteers he has gathered from mankind. This city is not the New Jerusalem, which appears after time is no more, this is an earthly city built with stone.