"Burning books and building fortifications are normal tasks for princes; the only thing unique about Shih Huang Ti was the scale of his work," writes Borges. (Quemar libros y erigir fortificaciones es tarea común de los príncipes; lo único singular en Shih Huang Ti fue la escala en que obró.)
He speculates that perhaps for Shih Huang Ti, building the wall to conquer space and burning the books to destroy past time were magic barriers meant to stop death.
Shih Huang Ti, según los historiadores, prohibió que se mencionara la muerte y buscó el elixir de la inmortalidad y se recluyó en un palacio figurativo, que constaba de tantas habitaciones como hay días en el año; estos datos sugieren que la muralla en el espacio y el incendio en el tiempo fueron barreras mágicas destinadas a detener la muerte.The "virtual fence" is a magical barrier in both space (the "fence" part) and time (it's "virtual" character is its transmission of signals that someone or some force has transgressed the barrier). Its magic would surely have puzzled Shih Huang Ti, though, because it is not directed against death, but against an even more powerful American obsession: the invasion of aliens. And its magic is as futile as the other. The Chinese emperor could not stop death and could not even stop fretting about it long enough to enjoy life. And the virtual fence is futile, because the aliens are already among us in space and their virtual incursion in time is, virtually, unstoppable.
Here's one place to find Jorge Luis Borges' 1950 essay, La muralla y los libros. And here it is in English, translated by Gaither Stewart: The Wall and the Books.