"Orientalist" literature, which is to say, highly fictionalized and romanticized depictions of Asian -- typically Middle Eastern -- cultures represent an important and often-unacknowledged influence on the development of the fantasy genre. Beginning in the 18th century, tales of "the East" became an increasingly common and accepted means by which Western writers could spin stories of exotic lands and strange customs. In many cases, the cultures depicted have minimal resemblance to genuine non-Western cultures, being effectively imaginary. While that may be a disappointment to readers looking to be schooled in these cultures through literature, Orientalist tales nevertheless gave writers the means by which to present stories whose cultural backgrounds weren't the standard European (generally medieval) stuff that was commonplace in the other precursors of fantasy.
William Beckford's 1786 novel, Vathek, is a good representative of Orientalist novels. Interestingly, the author, though an Englishman, wrote the novel in French, the English translation of which appeared first -- and anonymously -- while the French original appeared in 1787, with Beckford's name attached to it. Unlike earlier Oriental novels, Vathek includes a number explicitly supernatural elements, making it similar to Gothic novels, which were also fashionable at the time. The inclusion of these elements made Vathek both unique in its time and of lasting influence, with writers such as H.P. Lovecraft and Clark Ashton Smith both expressing admiration for it.
The novel tells the story of the caliph Vathek, who attempts to acquire supernatural powers for himself by means of various occult practices. Aiding Vathek in this quest is his mother, Carathis, who is in many ways an even more interesting character than her son. Like many novels of its time, Vathek is somewhat rambling, being in many ways a picaresque, in which the title characters wanders about, encountering many bizarre characters, undertaking similarly strange activities, and generally being buffeted about by circumstance as he attempts to achieve his goals of supernatural power. Of course, Vathek isn't a true Picaro; he's a rogue, certainly, but not with a heart of gold. Indeed, he's the kind of corrupt and self-aggrandizing authority figure whom Picaro would show up. Neither is he a bold rebel, flouting antiquated social conventions in the name of freedom of thought and action. He's closer to an anti-hero and is definitely a prototype for many of the doomed libertines you see in pulp fantasies of the early 20th century.
Vathek is filled with many references to Arabian and Islamic myth and legend, from genies to Eblis, ruler of the demons. As I said, the book's not a scholarly work; all of its elements exist to further the story that Beckford wants to tell. In that respect, I think it's actually a pretty good model for referees looking to add some exotic flavor to their campaigns without becoming overly obsessed with real-world details. And, despite its somewhat meandering storyline, Beckford manages to hold the reader's attention by making all the individual episodes of the larger tale interesting, from the caliph's attempts to decipher the writing on some glowing swords he purchased from a merchant to his encounter with some pious Muslim dwarves who attempt to show him the error of his occult ways.
Vathek is an enjoyable book, one that's of lasting interest to anyone looking into the origins of modern fantasy. It's in the public domain, of course, and available in many translations and degrees of completeness.