During the Trans-Saharan slave trade, slaves were transported across the Sahara desert. Most were moved from Sub-Saharan Africa to North Africa to be sold to Mediterranean and Middle eastern civilizations; a small percentage went the other direction. Estimates of the total number of black slaves moved from Sub-Saharan Africa to the Muslim world range from 11-17 million, and the trans-Saharan trade routes conveyed a significant number of this total, with one estimate tallying around 7.2 million slaves crossing the Sahara from the mid-7th century until the 20th century.