A city wall is a defensive structure built around a city to protect it from invasions and attacks. These walls were commonly constructed from stone, brick, or earth and often featured towers and gates for added security. Many ancient cities, such as Jerusalem and Rome, had impressive walls that served both military and symbolic purposes. In addition to their defensive role, city walls often defined the boundaries of urban areas. They facilitated trade and controlled movement in and out of the city. Today, remnants of these walls can be found in many historical cities, serving as a reminder of their past significance.