Early medieval Irish society was highly stratified, possessing a formalized ranking structure, and ritual played an important part in legitimizing the possession of rank and office, especially kingship. Power was ultimately dependent on physical force, but was maintained through the control of land, agricultural production, exchange, and—in particular—livestock. The basis of power, however, was inherently unstable. Although some kingdoms and dynasties exhibited powerful centralizing tendencies, political power was essentially transitory, a product of the pattern of royal succession and the segmentary nature of royal dynasties. According to Ó Corráin, “great overkingdoms are dismantled by fission and segmentation, and are built up again by later dynastic expansion and reconquest.”