During the reign of Emperor Qin Shi Huang, the notable structure built was the Great Wall of China. Although portions of the wall had been constructed earlier, Qin Shi Huang is credited with unifying various walls built by previous states into a comprehensive defensive fortification. The Great Wall served to protect against invasions from nomadic tribes to the north and as a means of controlling trade and immigration along the Silk Road. This monumental project reflects the emperor's ambition for unity and strength across his empire. The Great Wall remains one of the most iconic symbols of Chinese history and engineering.