Modern plantation slavery was introduced on the Kenya coast no earlier than the 1820s, but within decades slaves made up nearly 25 per cent of the population. Slavery preexisted the plantations, but in mild form. In the early nineteenth century slaves were owned by leading townsmen. The Mazrui governors of Mombasa were the largest slave owners, prior to their ouster by the Busaidi, and turned out large groups of slaves for public works and military service. Race consciousness among coastal freeborn is revealed in their notions of group descent. During the nineteenth century on the Kenya coast, the historical traditions of many established clans began to affirm southern Arabian or Omani origins. Rendered inferior by color, birth, and occupation, slaves were reduced to objects of abuse. European observers, mostly resident missionaries, witnessed many incidents of severe punishment and cruelty inflicted on slaves, especially in the towns. Events in the coastal hinterland constituted the more abrupt, and violent, change.