“By the Waters of Babylon” (1937)
Stephen Vincent Benét (writer).
Read in 2017.
The title probably alludes to psalm 137 of Psalms (ca. 700–200 BCE). This short story is a portal to all the post-apocalyptic science fiction that followed, where technical civilization has regressed to a pseudo-medieval level. It’s amazing that it came out in response to the Spanish civil war, before any public knowledge of the atomic bomb as real, though after H. G. Wells predicted the bomb in The World Set Free (1914).
References here: Always Coming Home (1985).