Why were ancient cities often densely populated and surrounded by walls?

In the context of social science and urbanization, ancient cities were characterized by high population density and defensive walls due to several interrelated factors:

• Defense and Security: Early cities were frequently subject to raids and armed conflict, making protection a primary concern. Because these settlements were often vulnerable, they were enclosed by walls to provide security for their inhabitants.12
• Spatial Constraints: It was difficult and costly to extend fortifications over large areas, which necessitated that people live in close proximity to one another within the protected perimeter. Consequently, urban design was limited by the need to remain within the range of a secure water supply and the defensive boundaries of the city walls.2
• Social and Economic Organization: The development of agriculture allowed for storable food surpluses, which could sustain higher population densities and support specialized labor. This concentration of people facilitated the growth of complex social, political, and religious institutions, often centered around a citadel or temple, which served as both a functional hub and a final line of defense.314