Half a century ago jazz was an obscure, regional American music. Today it can reasonably claim to be an international idiom. Jazz took shape in the southern part of the United States, the result of a fusion between Negro blues, ragtime and military march music, and for the past sixty years it has followed a pattern of development almost exactly similar to that of European music, but undertaken at a much more hectic speed. First came the beginning, in folk song. Next followed a polyphonic period, a period during which jazz evolved the New Orleans style of playing, with its improvising front line of trumpet, clarinet and trombone. The 1920s saw the introduction of written arrangements: on the one hand the organization of New Orleans jazz into a dramatic pattern by Jelly Roll Morton, the first authentic jazz composer; on the other, an increasing preoccupation with harmony, reflected in the growth of eleven- and twelve-piece ensembles. But for genuinely orchestral writing, jazz had to wait a few years longer, until Duke Ellington came to maturity as a composer, using timbres that were peculiar to the Ellington orchestra, building his scores around the talents of individual musicians.