: Features watchtowers for signaling (smoke/fire) and beacon towers for communication.
: Built to guard against nomadic invasions from the north, like the Mongols. Trade Control : Served as a checkpoint for the Silk Road . Timeline : The Great Wall
: Initial fortifications joined by Emperor Qin Shi Huang . : Features watchtowers for signaling (smoke/fire) and beacon
: Most visible stone sections were built during this era. 🛠️ Engineering Marvels The Great Wall