The beams and columns of the Forbidden City are built of wood, as are the walls that divide the hallways into distinct chambers. Wood was traditionally the preferred construction material in traditional Chinese architecture. The Forbidden City is the biggest collection of well-preserved medieval wooden buildings in the world. It was built between 1406 and 1420 for the early Ming emperor Tian Hou (Ming Huang), who lived through almost every major event of his country's history: the fall of the Yuan dynasty, the invasion of Japan, the outbreak of the Black Death, etc. Although the Forbidden City is often referred to as a "city", it was more like a large imperial palace or even a small European royal court with its own government officials. It was not considered safe to live there permanently. Instead, people went about their business within the walls while waiting for important matters to be resolved. There were no streets inside the city wall, only open spaces known as "Li" where trading took place by day and entertainment by night. Inside the city wall were over 100,000 square meters of land, which included gardens, forests, and farmlands. Here you would find all the necessities of life including food, cloth, medicine, and transportation. At any given time, there were probably only around 20,000 people living inside the city walls; the rest of China stayed safely outside our gates enjoying the peace and prosperity within.