How was the Great Wall of China built?

The Great Wall was built by many groups over centuries, using local earth, stone, brick, wood, and hard labor. Workers carried, rolled, lifted, packed, and fired materials where the wall crossed mountains, deserts, and borderlands.

The cleverest part is how the builders matched the land. Some stretches were rammed earth pressed tight in layers; later sections used brick and watchtowers, where soldiers could pass warnings quickly with smoke in daylight and flames after dark.