We have seen that human labor power is enabled at a very early stage of production to produce considerably more than is needed to maintain the producer. We have found that this stage coincided in general with the first appearance of the division of labor and of exchange between individuals. Now, it was not long before the great truth was discovered that man may himself be a commodity, and that human labor power may be exchanged and exploited by transforming a man into a slave. Hardly had exchange between men been established, when men themselves were also exchanged. The active asset became a passive liability, whether man wanted it or not. Slavery, which reaches its highest development in civilization, introduced the first great division of an exploited and an exploiting class into society. This division continued during the whole period of civilization. Slavery is the first form of exploitation, characteristic of the antique world. Then followed feudalism in the middle ages, and wage labor in recent times. These are the three great forms of servitude, characteristic of the three great epochs of civilization. Their invariable mark is either open or, in modern times, disguised slavery. The stage of commodity production introducing civilization is marked economically by the introduction of (1) metal coins and, thus, of money as capital, of interest, and of usury; (2) merchants as middlemen between producers; (3) private property and mortgage; (4) slave labor as the prevailing form of production. The form of the family corresponding to civilization and becoming its pronounced custom is monogamy, the supremacy of man over woman, and the monogamous family as the economic unit of society. The aggregation of civilized society is the state, which throughout all typical periods is the state of the ruling class, and in all cases mainly a machine for controlling the oppressed and exploited class. Civilization is furthermore characterized on one side by the permanent introduction of the contrast between city and country as the basis of the entire division of social labor; on the other side by the introduction of the testament by which the property holder is enabled to dispose of his property beyond the hour of his death. This institution is a direct blow at the gentile constitution, and was unknown in Athens until the time of Solon. In Rome it was introduced very early, but we do not know when.[45] In Germany it was originated by the priests in order that the honest German might bequeath his property to the church without any interference.