One of the earliest pieces of military literature is "The Art of War", written by Chinese general Sun Tzu in the 6th century BC. This book contained a detailed explanation and analysis of the Chinese military, from weapons and strategy to rank and discipline. Sun Tzu also stressed the importance of intelligence operatives and espionage to the war effort. Because Sun Tzu has long been considered to be one of history's finest military tacticians and analysts, his teachings and strategies formed the basis of advanced military training for centuries to come.