(Here's a specific fancy dress event theme that is basically a genteel Edwardian toga party, despite the author's efforts to depict it as educational.)
Some of the most successful fancy-dress parties as to costume, and most fascinating as to the amusement afforded, have been arranged by limitations as to books, eras, countries, etc., which have been mentioned by the hostess upon the cards of invitation. For instance, she invites her friends and acquaintances to...a classic party, the latter including both Greeks and Romans, a few of the most presentable of the gods and goddesses and so on, down to the characters portrayed in Hawthorne's "Marble Faun."
Both the Greek and Roman costumes of the free men and women are a most interesting study well worth giving a party for, if only for that; while following such a research, one's memory of classic times is refreshed, if not newly stored with historic facts, regarding tastes and habits that have influenced all the succeeding generations of civilized peoples. Gentlemen and ladies who carry themselves with dignity can wear these vestments with charming and novel effects, that contrast curiously with the appointments of a modern drawing-room.
Masquerades, Tableaux and Drills. New York: The Butterick Publishing Company, 1906.