Children's literature can be traced to stories and songs, part of a wider oral tradition, that adults shared with children before publishing existed. The development of early children's literature, before printing was invented, is difficult to trace. Even after printing became widespread, many classic "children's" tales were originally created for adults and later adapted for a younger audience. Since the fifteenth century much literature has been aimed specifically at children, often with a moral or religious message. The late nineteenth and early twentieth centuries is known as the "Golden Age of Children's Literature", because many classic children's books were published then.