Roman walls were fortifications built by the ancient Romans to protect their cities and territories. These walls were made of stone, brick, or earth and often included towers and gates for defense. They served to keep out invaders and control access to the city, playing a crucial role in the security of Roman settlements. One of the most famous examples of Roman walls is the Aurelian Walls in Rome, which were constructed in the 3rd century AD. Other notable examples include the Hadrian's Wall in Britain, which marked the northern boundary of the Roman Empire, showcasing the engineering skills of the Romans in military architecture.