If trova was the first native Cuban folk music, then son was the first Afro-Cuban musical form. Son was essentially a marriage of syncopated African rhythms and percussion with trova's Spanish-derived melodies and string instruments. The music and its accompanying dance moves developed in eastern Cuba, particularly the Oriente province, around the beginning of the 20th century, and by the end of World War I, son had become quite popular in Havana despite its lower-class, multi-ethnic origins. In its most commonly accepted form, son was performed by a septet featuring trumpet, guitar, bass, tres (a nine-string guitar-like instrument), bongos, maracas, and the all-important time-keeping clavés; usually, at least one or two of the musicians doubled as vocalists. The clavé pattern of the son form typically covered two measures of four beats apiece, striking three times during the first measure and twice in the second (or, sometimes, vice versa). As son's popularity grew among higher social classes during the '30s, musicians began to move toward a more smoothed-out, genteel sound; around the same time, composer Moisés Simóns scored a huge international hit with his son "El Manisero" ("The Peanut Vendor"), igniting a passion in the United States for Afro-Cuban dance music. (Much of what Americans referred to as "rumba" during this time was actually son.) In the early '40s, son bandleader and tres player Arsenio Rodriguez invented a variation on the form called the son montuño, which often reversed the typical clavé pattern, was taken at a slightly more deliberate tempo, and (similar to the guaracha) added a section called the montuño, which featured call-and-response improvisation by the lead vocalist over a chorus vamp (plus, sometimes, instrumental solos). The spontaneity of son montuño renewed the spark of the original form, and laid the groundwork for the mambo explosion that was to come shortly; it was also a central component of both Afro-Cuban jazz and salsa. Although son is rarely performed exclusively anymore, it remains a strongly rooted tradition that Latin musicians still look to in order to refresh and renew their music.