What were the three major components of the Great Wall’s fortification system?

The Great Wall of China fortification system was composed of three major elements:1

• Passes: These served as major strongholds at key locations, such as trade route intersections. They featured gate towers for command and surveillance, access ramps for troops, and defensive structures like the wengcheng to shield gates from direct assault.1
• Signal towers (beacons): These structures were integrated into the defense system to facilitate communication and monitor enemy movements.1
• Walls: These formed the primary defensive barrier, constructed using various materials—such as stone, brick, and tamped earth—depending on the local terrain and available resources.12