The Great Wall is a series of stone and earthen fortifications in China, built from the 5th century BC to the 16th century AD. The length of the Great Wall varies according to different sources, but it is generally believed to be around 21,196 km (13,171 miles). In English, you can say \"The Great Wall\'s length is approximately 21,196 kilometers (13,171 miles)\" or simply \"The Great Wall is 21,196 kilometers (13,171 miles) long.\"