By the water of babylon

I always thought that the first clue that this is a post-apocolyptic story is the mention of metal. Early in the story we are informed that there is metal in the houses of the Gods, and that the metal is dangerous. Metal is salvaged because it is special and useful.

It is forbidden to go to any of the Dead Places except to search for metal and then he who touches the metal must be a priest or the son of a priest. Afterwards, both the man and the metal must be purified.