The Mossi are farmers and herdsmen. They are unique in Burkina Faso for their centralized and hierarchical political system, in addition to clans and professional corporations led by elders. At the apex of the political system is the Moro Naba, or Emperor of the Mossi, whose palace is in Ouagadougou. The rulers use wooden figures to validate political power, while the commoners use masks to honor the spirits of the wilderness. The masks embody spirit powers, nature spirits of the sort found among many farming peoples. In some regions masks are housed within ancestral shrines during periods when they are not being danced, to be augmented by ancestral powers that control the earth and productivity, all in the well-being of the people and their natural environment. Thekaranga masks appear during funeral occasions to accompany the dead to their tombs, at agricultural rites, and other important community events. Their task is also to protect wild plants, whose use is collectively regulated.