From the 8th century, one of the main musical centers of the Arabic nation besides the key places Damascus and Baghdad, was Spain. When Arabs began to expand in southern Spain, two different cultures "crashed" themselves, and then the fusion developed in a variety of cultural issues. Regarding music, this fusion was known as Andalusian or Moorish branch of Islamic music.
Ziryab was the main figure of this development. A gifted pupil of Ishaq al-Mawsili, he had to migrate from Baghdad to Spain because he got advantage over his teacher (a severe offense, then and nowadays). He was settled in the court of Cordoba under the amir Abd al-Rahman II of the Umayyad Dynasty (822-52). There he made a whole revolution regarding music: he was an amazing singer, created a famous school of music, and made one of the main changes on ouds: to add a fifth (G) bass string.
Regarding musical theory, he rearranged it completely, setting free the metrical and rhythmical parameters and creating new ways of expression (mwashah, zajal, and nawbah -suite-).
Besides, he also brought other values of the Baghdad culture to al-Andalus, including etiquette, cooking, fashion, and toothpaste among others.
Thanks to Beth Forrest, Ph.D. candidate in History of Boston University, for her help.