The first slaves were prisoners taken in war and the majority of slaves appeared to be owned by kings, priests and temples, and only a relatively small percentage were in private possession, which is not the case in the transatlantic trade of slaves. The Arab Zanj and Bantu slave trade in southeast Africa is one of the oldest slave trades; it was believed that slaves were sold from the Zanzibar slave market to the Somali coast. Zanj brought as slaves to the Middle East were often used in strenuous agricultural labor. As the plantation economy boomed and Arabs became wealthy, farming and other manual labor was thought to be demeaning. Male slaves were often employed as servants, soldiers, or laborers, while female slaves were long traded in Middle Eastern countries and kingdoms by Arab and Oriental traders as concubines and maids. In terms of legal considerations, Bantu slaves were devalued. Somali social customs strongly discourage, censor and despise any type of sexual contact with Bantu slaves. David Livingstone, a Scottish missionary explorer, wrote about the slave trade in the Great Lakes region of Africa, which he visited in the mid-19th century.