“La Folia” seems to have appeared first as a folk-dance tune in late medieval Portugal. Over the next century, it spread to Spain and Italy and composers started adapting it; in the 17th and 18th centuries, “La Folia” and variations on it were all over the place (even colonial Latin America). Today some of those old pieces are being heard in concert again, while the melody turns up in pop songs and The Addams Family‘s theme, often without contemporary musicians knowing where it came from. – BBC