♪ as the sun set over the moroccan town of essaouira, the huge crowd grew more impatient. el kasri's backup singers came on first, wearing the same ornate silk robes and tasseled fezzes the gnawans have worn for hundreds of years. finally, the maalem, or master musician, appeared and strapped on his gimbri. the mother of all basses, the gimbri is made from wood, camel skin, and strung with goat gut. el kasri started slowly. one of morocco's top maalems, hamid el kasri helped make gnawa a contemporary force. soon he picked up the pace. ♪ the arabic lyrics date from the middle ages, and this crowd knew every word. ♪ the music built to a crescendo. it was a pyramid of sound driven by the pulsating beat of the krakebs, metal castanets that are played at astonishing speed. this is the musical legacy of enslaved black africans brought to morocco in medieval times. [ cheers and applause ] but the story doesn't end here. it's music that traveled out into the atlantic from the slave ports of africa and helped give rise to the american blues. >> this was a point of departure. it was