Although it is often mistakenly thought of as a single wall, the Great Wall is a series of walls that were constructed, reconstructed and expanded over several centuries and, depending on the location, using different materials. The massive construction project was the idea of China’s first emperor, Shi Huangdi, who ended more than 250 years of regional fighting between several independent states, and united China. Once in control, Shi Huangdi wanted to maintain his power and position. The idea to create a massive wall along the northern border of the country was conceived by the emperor to bar assailants from kingdoms to the north of China. Construction of the Great Wall continued long after the reign of Shi Huangdi, particularly during the Han and the Ming dynasties. During these periods, features such as watch towers, gates and garrisons were added or enhanced and the Wall’s design was unified (Marsh, 2006).