AL-MANSUR
Abu Ja'far Abdallah ibn Muhammad al-Mansur. And al-Rahman had assembled a very powerful army of blond, blue-eyed Slavic slaves supplemented with black African warriors. The Caliph, was always concerned when one of his subjects had an effective fighting force as he might be a rival. But if the troops were Muslims the danger was not so great as there was a built in loyalty to the Caliph. However, in this case, the fierce fighters were not Muslims. Hence the sea was a desirable barrier.
Al-Mansur or Abu Ja'far Abdallah ibn Muhammad al-Mansur (/ælmænˈsʊər/; Arabic: أبو جعفر عبدالله بن محمد المنصور; 95AH – 158 AH was the second Abbasid Caliph reigning from 136 AH to 158 AH (754 AD – 775 AD) and succeeding As-Saffah. He is known for founding the 'Round City' of Madinat al-Salam which was to become the core of imperial Baghdad.