Slavery in the Muslim world first developed out of the slavery practices of pre-Islamic Arabia,[1] and was at times radically different, depending on social-political factors such as the Arab slave trade. Throughout Islamic history, slaves served in various social and economic roles, from powerful emirs to harshly treated manual laborers. Early on in Muslim history they were used in plantation labor similar to that in the Americas, but this was abandoned after harsh treatment led to destructive slave revolts,[2] the most notable being the Zanj Rebellion of 869–883.[3] Slaves were widely employed in irrigation, mining, and animal husbandry, but the most common uses were as soldiers, guards, domestic workers, [2] and concubines. Many rulers relied on military slaves, often in huge standing armies, and slaves in administration to such a degree that the slaves were sometimes in a position to seize power. Among black slaves, there were roughly two females to every one male.[2] Two rough estimates by scholars of the number of slaves held over twelve centuries in the Muslim world are 11.5 million[4] and 14 million,[5][6] while other estimates indicate a number between 12 and 15 million slaves prior to the 20th century.[7] Manumission of a Muslim slave was encouraged as a way of expiating sins.[8] Many early converts to Islam, such as Bilal ibn Rabah al-Habashi, were former slaves.[9][10][11][12] In theory, slavery in Islamic law does not have a racial or color component, although this has not always been the case in practice.[13] In 1990, the Cairo Declaration on Human Rights in Islam declared that "no one has the right to enslave" another human being.[14] Many slaves were often imported from outside the Muslim world.[15] Bernard Lewis maintains that though slaves often suffered on the way before reaching their destination, they received good treatment and some degree of acceptance as members of their owners' households.[16] The Arab slave trade was most active in West A