The World's 7 Wonders Need to Be on Your Bucket List

Though the Great Wall was designed to keep northern invaders out, it served more as a powerful symbol than an effective defense system. Construction began in 220 BC under Qin Shi Huang and continued through the 17th century AD, becoming more than 12,000 miles long. Starting in Shanhaiguan and ending in Jiayuguan, the structure was entirely handmade and can be seen from the moon.