Yemeni Akhdam, or servants, are similar to hereditary castes, but are distinguished by their African features and the menial jobs they perform.
Widespread prejudice places the Akhdam at the bottom of Yemen's social ladder.
Asked about the origins of the Akhdam, Yemenis say they are descendants of Ethiopians who crossed the Red Sea to conquer Yemen before the arrival of Islam some 1,400 years ago - making them outsiders in their own country.
Most live in slum areas in the outskirts of the capital Sanaa and other main cities. They reside in small huts haphazardly built of wood and cloth, without basic services such as running water, electricity and sewage networks.
* Reuters