Great Wall

The Great Wall of China is actually four great walls rather than a single, continuous wall. The oldest section was begun in 221 b.c., not long after China was unified into an empire out of a loose configuration of feudal states. Collectively, they stretch from Liaodong in the east to Lop Lake in the west, from the present-day Sino–Russian border in the north to Tao River in the south; along an arc that roughly delineates the edge of the Mongolian steppe; spanning over 20,000 km (12,000 mi) in total. Today, the defensive system of the Great Wall is generally recognized as one of the most impressive architectural feats in history.