Cities, characterized by population density, symbolic function, and urban planning, have existed for thousands of years. In the conventional view, civilization and the city both followed from the development of agriculture, which enabled production of surplus food, and thus a social division of labour (with concomitant social stratification) and trade. Early cities often featured granaries, sometimes within a temple. A minority viewpoint considers that cities may have arisen without agriculture, due to alternative means of subsistence (fishing), to use as communal seasonal shelters, to their value as bases for defensive and offensive military organization, or to their inherent economic function. Cities played a crucial role in the establishment of political power over an area, and ancient leaders such as Alexander the Great founded and created them with zeal.