Classic Chinese architecture refers to a style of architecture that has taken shape in East Asia over many centuries. The structural principles of Chinese architecture have remained largely unchanged, the main changes being only the decorative details. Since the Tang Dynasty, Chinese architecture has had a major influence on the architectural styles of Korea, Vietnam, and Japan. The yellow roof tiles and red walls in the Forbidden City (Palace Museum) grounds in Beijing, which were built during the Yongle era (1402–1424) of the Ming Dynasty, include examples of certain architectural features that were reserved solely for buildings built for the Emperor of China. Yellow was the Imperial color, so yellow roof tiles still adorn most of the buildings within the Forbidden City. An important feature in Chinese architecture is its emphasis on articulation and bilateral symmetry, which signifies balance. Bilateral symmetry and the articulation of buildings are found everywhere in Chinese architecture, from palace complexes to humble farmhouses. The projected hierarchy and importance and uses of buildings in traditional Chinese architecture are based on the strict placement of buildings in a property/complex. Buildings with doors facing the front of the property are considered more important than those facing the sides. Buildings facing away from the front of the property are the least important.