Civilizations all share five characteristics, all of which are very clearly exemplified in cities and urban centers. These five characteristics are;
1) Advanced Cities: Urbanization is one of the characteristics itself. Tribes or nations that exhibit a certain degree of city building are considered civilizations.
2) Specialized Workers: Specialization of labor is easily observed in cities. Metalworkers, food producers, merchants and so forth are all vital to the creation of city workers.
3) Record Keeping: Written records are usually most highly concentrated in cities. Libraries as well as records used in trade or religious ceremonies were a typical fixture in cities.
4) Advanced Technologies: Centers of technological development were usually centered in urban centers in order to capitalize on specialization of labor as well as financial resources. Technology was also used extensively within cities to help with sanitation, architecture and defense.
5) Complex Institutions: Institutions of a military and religious nature were always centered around large population centers, like cities.