City walls are fortifications built around a city to protect it from invasions and attacks. They were commonly constructed from stone, brick, or earth and often included towers and gates for defense. Many ancient cities, such as Jerusalem and Rome, had impressive walls that served both practical and symbolic purposes. Over time, as warfare evolved and cities expanded, the need for city walls diminished. Today, remnants of these walls can be found in many places, serving as historical landmarks. Some cities, like Carcassonne in France, still have well-preserved walls that attract tourists and showcase their rich history.