White slavery refers to the enslavement of any of the world's European ethnic groups throughout human history, whether perpetrated by non-Europeans or by other Europeans. Slavery in ancient Rome was frequently dependent on a person's socio-economic status and national affiliation, and thus included European slaves. It was also common for European people to be enslaved and traded in the Muslim world; European women, in particular, were highly sought-after to be concubines in the harems of many Muslim rulers. Examples of such slavery conducted in Islamic empires include the Trans-Saharan slave trade, the Barbary slave trade, the Ottoman slave trade, and the Black Sea slave trade, among others.