“The Empire never ended,” Fat quoted to himself. That one sentence appeared over and over again in his exegesis; it had become his tag line. Originally the sentence had been revealed to him in a great dream. In the dream he again was a child, searching dusty used-book stores for rare old science fiction magazines, in particular Astoundings. In the dream he had looked through countless tattered issues, stacks upon stacks, for the priceless serial entitled “The Empire Never Ended.” If he could find it and read it he would know everything; that had been the burden of the dream.
Prior to that, during the interval in which he had experienced the two-world superimposition, had seen not only California, U.S.A., of the year 1974 but also ancient Rome, he had discerned within the superimposition a Gestalt shared by both space-time continua, their common element: a Black Iron Prison. This is what the dream referred to as “the Empire.” He knew it because, upon seeing the Black Iron Prison, he had recognized it. Everyone dwelt in it without realizing it. The Black Iron Prison was their world.
Philip K. Dick, "Valis"