"The Romans recognized under the law of nations (ius gentium) a fundamental distinction between free and non-free. The non-free were legally the chattels of their owners, and their participation in society was limited. Even here there was a hierarchy; household slaves and slaves who worked in their masters business were in a much better position than farm workers, or worst of all those who worked in the state-run mines. Slaves of the emperor were at the top of the enslaved social tree with opportunities for advancement in the emperors service. Servile status came about through capture in war, or the activities of slave-dealers, or by birth, in that children born to a slave mother would be slaves (vernae). There were also cases of self-enslavement for particular motives, often involving fraud (no. 3)"--.