"Archetypes" (also known as "Etos Kosmou 6825") is a short story by Harry Turtledove, first published in Amazing, November, 1985. It is a story set in the Agent of Byzantium series, and was reprinted in the fix-up novel of the same name in 1987.
It is 1316 and the Persians are trying to sow discord in Mesopotamia. Hundreds of posters appeared overnight in the town of Daras advocating Nestorians and Monophysites to rise up against the oppression of the orthodox faith and change their allegiance to the King of Kings. It would have taken dozens of scribes to produce this many posters but no sign of a conspiracy this large existed. Basil Argyros was sent to investigate.