The Haratin of Mauritania, states Joseph Hellweg – a professor of Anthropology specializing on West African studies, were part of a social caste-like hierarchy that likely developed between 1300 to 1500 CE because of a Bedouin legacy. The "Hassan" monopolized the occupations related to war and politics, the "Zwaya" (Zawaya) the religious roles, the "Bidan" (White Moors) owned property and held slaves (Haratins, Black Moors), and the slaves constituted the lowest of the social strata. Each of these were castes, endogamous, with hereditary occupations and where the upper strata collected tribute ("horma") from the lower strata of Mauritanian society, considered them socially inferior, and denied them the right to own land or weapons thereby creating a socio-economically closed system.