The construction of the Great Wall of China dates back to the third century BC, and many of the fortresses in the wall date back hundreds of years. Before that, China was divided into a number of kingdoms during the Warring States Period. Around 220 BC. Qin Shi Huang, the first king of the United China, ordered the removal of ancient fortresses, the merging of ancient fences along the northern border and the construction of a single wall of more than 5,000 kilometers to protect China from attacks from the north.