Musical introduction to a larger, often dramatic, work. Originating with Claudio Monteverdi's Orfeo (1607), overtures served as openings for operas. The large-scale two- or three-part French overture invented by Jean-Baptiste Lully (1658) for his operas and ballets was widely imitated for a century. The sinfonia, the standard Italian overture form in the late 17th and 18th centuries, was a principal precursor of the three-part sonata form and thus provided the model for the earliest symphonies, which consisted of three movements. In the 19th century, overtures independent of any larger work usually illustrated a literary or historical theme (seesymphonic poem). Overtures to operettas and musicals have traditionally been medleys of their themes.