The Seven Wonders of the Ancient World were

4. Great Wall of China

The Great Wall of China spans from Dandong to Lop Lake, in an arc that runs from east to west, roughly parallel to ancient China's northern border. Construction began in multiple locations in the seventh century BC; these walls were later joined together and fortified. The wall has been destroyed, rebuilt and maintained numerous times over the centuries, with the majority of the existing structure dating back to the Ming Dynasty of the fourteenth to seventeenth centuries. Built to withstand raids and invasions by the Eurasian nomads, the Great Wall was built from stone, brick, wood, and packed earth, among other materials. In areas most vulnerable to attack, fortifications were enhanced with military housing and stations, watch towers, and smoke-signalling stations. The wall was also utilized for emigration control, commerce, and trade regulation.