"The Gold-Bug" includes a simple substitution cipher. Though he did not invent "secret writing" or cryptography (he was probably inspired by an interest in Daniel Defoe's "Robinson Crusoe"), Poe certainly popularized it during his time. To most people in the 19th century, cryptography was mysterious and those able to break the codes were considered gifted with nearly supernatural ability. Poe had drawn attention to it as a novelty over four months in the Philadelphia publication "Alexander's Weekly Messenger" in 1840. He had asked readers to submit their own substitution ciphers, boasting he could solve all of them with little effort. The challenge brought about, as Poe wrote, "a very lively interest among the numerous readers of the journal. Letters poured in upon the editor from all parts of the country." In July 1841, Poe published "A Few Words on Secret Writing" and, realizing the interest in the topic, wrote "The Gold-Bug" as one of the few pieces of literature to incorporate ciphers as part of the story. Poe's character Legrand's explanation of his ability to solve the cipher is very like Poe's explanation in "A Few Words on Secret Writing".