As we talk about in "What's Up with the Title?," the first detective agency in the world was founded in Paris by a man Poe admires enough to the guy a shout-out in "The Murders in the Rue Morgue": François Vidocq. So setting this story in Paris gives a clear lineage from Vidocq, first real detective, to Dupin, first fake detective.
But here's something that grabbed our attention. Poe probably never actually visited Paris. Nevertheless, in a short story where the narrator won't even tell us when the tale's taking place (18–? What?), it's striking that it's really specific about where everything's happening. Think about it: Dupin and the narrator meet at a library on the Rue Montmartre (remember, "rue" = "street" in French). (See here for more information on this section of Paris, famous for its artist communities in the 19th and 20th centuries.) The place Dupin and the narrator share is a "time-eaten and grotesque mansion" in an unfashionable and out-of-the-way part of the Faubourg St. Germain (an old-fashioned but still relatively aristocratic part of the Left Bank in Paris). And the fictional Rue Morgue is placed in a real section of Paris, the Quartier St. Roch (source). So, what's going on? How come Poe is being so precise about the setting of this otherwise pretty hard to place story?
Well, we can't say for sure, but we have some guesses. First of all, Paris is pretty sexy. No, seriously, we think this is probably a factor. After all, all of the sections of Paris mentioned in the story have old aristocratic connections that make the Paris Poe describes seem exciting to us. There's Montmartre – the fact that the narrator and Dupin meet in this neighborhood would've signaled to anyone who knows Paris that they're both probably sensitive, Bohemian artist types. (Even Dupin's "grotesque mansion" suggests a great past gone to ruin, which is in line with Poe's Goth thing.) And the revolutionary artistic and intellectual activity of Paris probably seemed pretty awesome to someone trying to break into resistant literary circles in Baltimore, New York, and Boston.
But even beyond the fact that Paris probably seemed exotic to our friend Poe, there's also the fact that it was one of the great 19th century cosmopolitan centers, a place where many people of different ethnicities and nationalities lived side by side. This point is surprisingly important to the plot of "The Murders in the Rue Morgue": after all, there wouldn't have been that many European cities in 1841 that could believably have hosted an Ourang-Outang. And think of the testimony we receive – not just from French men and women, but from an Italian, an Englishman, a Dutch man, and a Spaniard. Add to this motley assortment of nationalities, the fact that Madame L'Espanaye's apartment has spoons made of Algiers metal (Algiers being the capital of Algeria, in northern Africa), and our French sailor has just managed to come back from Borneo as a member of a Maltese ship crew.
Part of the appeal of this setting is that Poe can believably squeeze in numerous unfamiliar people into one neighborhood. Since one of Dupin's great gifts is the observation of human faces and behaviors, he needs a city that can give him lots of opportunity for practice. With new populations traveling to the city everyday on its brand new railway lines, Paris in the 1840s (and, actually, still today) would've been one of the best places in the world for people watching – and for playing Dupin's games of creative deduction.