The identity of the Builders is a secret lost to time in Jorg’s day, though their surviving buildings, tunnels, and roads are widely used. Since the story takes place in a world a millennium following the Builder’s self-immolation in the Day of a Thousand Suns, it is strongly hinted that the Builders’ civilization is our own, contemporary civilization. The Day of a Thousand Suns, which one infers was a global nuclear war, takes place at a time when technology is at least somewhat more advanced than our own take for example the AI interface at the armory door or the Lichway, which has not required maintenance in over a thousand years.

Even so, the Builder ruins described by Jorg sound very familiar. Builder-stone, which Jorg describes as having been “poured and shaped using arts long forgotten” (111), is clearly concrete, and the rods of Builder-steel which reinforce Builder-stone must be rebar. Likewise, the heavy steel door blocking the way into the armory beneath the Castle Red is described in terms very similar to the doors used for modern bank vaults. The vertical shafts the Builders put into their concrete structures, which so puzzle Jorg in Chapter 29, are probably elevator shafts, though, given the nature of the facility into which the Castle Red has been built, it is also possible that they are nuclear missile siloes.