Classes, class interests and class lines are a part and parcel of all civilizations. They are less rigid and more flexible than similar lines existing in an agrarian community where land ownership plays so large a role in determining social forms and social functions. In a static agrarian community dominated by landlords, war-lords and the clergy, rigid class lines help to hold the community together. In a community dominated by business interests, both labor power and purchasing power must be free to respond to demand and supply. This is as true in a planned public economy as it is in a private enterprise economy. In accordance with the same principle, facilities are provided for the movement of individuals back and forth across class lines. The specialized, interdependent structure of civilization with its city control of the hinterland, its products and inhabitants, enabled the city-centered oligarchy to accumulate and concentrate wealth and monopolize power, to skim the cream from the available milk, monopolize the cream, distribute the skimmed milk judiciously and thus perpetuate its ascendancy through generations and centuries. During periods of expansion civilized communities develop a dynamism which maintains their ascendancy. In subsequent periods of contraction form takes over, imposing conformity on the status quo. During their periods of expansion civilizations are dynamic. Their history records growth at home, expansion abroad, exploitation, domestic and foreign under the pressure of effective motivating forces. The resulting dynamism leads to the contradictions, confrontations and conflicts which have studded the internal and external life story of every civilization. Perhaps the most outstanding aspect of the dynamic functioning of civilization is its growth in magnitude. It might be more accurate to describe the process as an explosive expansion--explosive because rapid and spectacular. Form limits function. At the same time function modifies and ultimately determines form. The two factors are omnipresent and complementary. Except for purposes of analysis they are two inseparable aspects of every human society. Where form predominates, social status results. Where function predominates fluidity, flexibility and dynamism are the outcome. Rapid change occurs on the home front at the same time that it is taking place abroad. Growth at home takes place in two fields. The first is the extension of the homeland frontiers, broadening the geographical area of the nucleus around which the civilization is being built. The second aspect of growth involves an increase in multiplicity, variety and complexity and perhaps also a higher level of quality. Increase in quality is an optional feature of growth and expansion. Toward the end of a cycle of civilization quality declines.