Erotic literature comprises fictional and factual stories and accounts of human sexual relationships which have the power to or are intended to arouse the reader sexually. Such erotica takes the form of novels, short stories, poetry, true-life memoirs, and sex manuals. A common feature of the genre is sexual fantasies on such themes as prostitution, orgies, homosexuality, sadomasochism, and many other taboo subjects and fetishes, which may or may not be expressed in explicit language. Other common elements are satire and social criticism. Despite cultural taboos on such material, circulation of erotic literature was not seen as a major problem before the invention of printing, as the costs of producing individual manuscripts limited distribution to a very small group of readers. The invention of printing, in the 15th century, brought with it both a greater market and increasing restrictions, like censorship and legal restraints on publication on the grounds of obscenity. Because of this, much of the production of this type of material became .