When why and where was the Great Wall of China built?

The Great Wall of China was built over several centuries, beginning in the 7th century BC and continuing until the 17th century AD. The wall was primarily constructed to protect the Chinese Empire from invasions by nomadic tribes from the north. It was also used as a means of controlling trade and immigration, and as a way to unify the Chinese people.

The wall was built in several sections, with construction often taking place in response to specific threats. The earliest sections were built by the Qin dynasty in the 3rd century BC, and the wall was extended and rebuilt by subsequent dynasties. The most famous section of the wall, known as the Badaling section, was built in the 16th century during the Ming dynasty.

The Great Wall of China is located in northern China, stretching across several provinces and autonomous regions. The wall's total length is estimated to be over 6,350 kilometers (3,945 miles). It is one of the most recognizable structures in the world, and is considered to be one of the greatest engineering feats in history.