Beijing (formerly romanized as Peking) is the capital of the People's Republic of China and the world's third most populous city proper. It is also one of the world's most populous capital cities. The city, located in northern China, is governed as a direct-controlled municipality under the national government with 16 urban, suburban, and rural districts. Beijing Municipality is surrounded by Hebei Province with the exception of neighboring Tianjin Municipality to the southeast; together the three divisions form the Jingjinji metropolitan region and the national capital region of China. Beijing is the second largest Chinese city by urban population after Shanghai and is the nation's political, cultural, and educational center. It is home to the headquarters of most of China's largest state-owned companies, and is a major hub for the national highway, expressway, railway, and high-speed rail networks. The Beijing Capital International Airport is the second busiest in the world by passenger traffic. The city's subway network is among the longest and busiest in the world. The city's history dates back three millennia. As the last of the Four Great Ancient Capitals of China, Beijing has been the political center of the country for much of the past eight centuries. The city is renowned for its opulent palaces, temples, parks, gardens, tombs, walls and gates, and its art treasures and universities have made it a center of culture and art in China. Encyclopædia Britannica notes that "few cities in the world have served for so long as the political headquarters and cultural centre of an area as immense as China." Beijing has seven UNESCO World Heritage Sites – the Forbidden City, Temple of Heaven, Summer Palace, Ming Tombs, Zhoukoudian, as well as parts of the Great Wall and the Grand Canal. Beijing hosted the 2008 Summer Olympics and was chosen to host the 2022 Winter Olympics, which will make it the first city to ever host both events.