How was slavery a part of ancient persia civilization

Slavery was a major part of any ancient civilization. Most of them relied on a steady supply of slaves who would have to work for free and on different aspects of civilized life that needed to be done (farming, taking care of things around houses of their masters, building different structures, etc.) Most of the work that required big amounts of labor force was done by slaves in general. This is probably the main way how slavery was playing a major part in ancient Persia.