The Great Wall, a communication system as well as a barrier.
About the Art of War
About 2,000 years ago, China was in turmoil. A series of wars left a third of the population dead and the leaders in search of a new way of governing. Confucius and Lao Tzu had developed their solutions but Sun Tzu's philosophy, born of his direct experience of war also gained a popular following amongst the ruling class. In the Art of War, Sun Tzu recommended a strategic method to win that rarely required actual war. Spies, diplomats, deception, and a correctly organised internal structure were his main tools. If it came to war though, he had detailed insight into its methods and strategies.
Around 1600AD in Japan, a samurai named Miyamoto Musashi emerged that was literally unbeatable. One time, using his two sword technique, he single-handedly beat over 30 samurai simultaneously attacking him with guns, arrows and swords. The rulers asked him to explain is strategies in writing. Alone in a cave he wrote The Book of Five Rings, a classic that is still used by modern executives and martial artists.