The Great Wall of China was built over several centuries, beginning in the 5th century B.C. during the Zhou dynasty. It was used to protect the country from invasions by nomads from the northern steppes. The wall known today is mainly the result of reconstructions carried out during the Ming Dynasty in the 14th century. The Great Wall of China has a total length of more than 21,000 km and is considered one of the wonders of the ancient world.