When was the Great Wall built?

The Great Wall was not built in a time, it’s the efforts of thousands of Chinese in many dynasties. These walls stretch over many thousands of miles in total, and stand in various stages of disrepair or restoration. The origin of the wall can date back to 7th century BC when there were many ducal states fighting against each other. Each ducal states or kingdoms built their own city walls to protect themselves.   In 221 BC, the King of Qin Kingdom conquered the other states and unified the whole country as Qin Empire, and the King became Emperor Qinshihuang (First Emperor of the Qin Dynasty). Emperor Qinshihuang ordered to link all city walls in different places up, and the Qin Dynasty Great Wall came into being. Little of the Qing Dynasty wall remains.   Later dynasties sometimes restored and rebuilt along a line established by their predecessors.

The Han Dynasty (206 BC-220 AD) was the second climax to repair the wall since it’s threatened by the Huns in the north at that time. The wall was reconstructed and maintained through the dynasty for almost 400 years. The later Sui, Northern and Jin dynasties all repaired, restored or expanded sections of the wall to defend themselves.   The Great Wall was revived again during the Ming Dynasty (1368-1644) following the collapse of Mongolian Yuan Dynasty. The Ming adopted a new strategy to keep Mongolians out by constructing walls along the northern border of China. The Ming construction was stronger and more elaborate due to the use of stone and bricks instead of rammed earth. Sections near the Ming capital of Beijing were especially strong. When the Ming was defeated by Manchurian in 1644, the Great Wall lost its function as defense project as the Qing Dynasty (1644-1911) controlled both the outside and inside of the wall. Most of sections of the Great Wall we see today were from the Ming Dynasty

What's the Great Wall like in ancient times?

Soldiers were stationing on the wall to keep watching the enemy outside of the wall. When the enemy were approaching, they would deliver the message by beacon towers with smoking at daytime and lighting at night. Most of farmers near the present-day wall are descendants of those wall-watchers.

How to build the Great Wall? What's the building material? What's the construction of the Great Wall?

The Great Wall was made by hands only without any modern machines. Most of the artisans were criminals who were punished by the law. The wall stretches from east to west by mountains, valleys, rivers and deserts, thus the building material were from the local area. Rammed earth, sands, willow trees, stones and bricks were all used in different sections of the wall. The earlier Qin and Han walls were small and low, and the Ming Great Wall were much higher and stronger than before. Watch towers, beacon towers, passes, garrison towns, fortresses and barrier wall combined a effective defense system.