China, officially the People's Republic of China (PRC), is a country in East Asia. It is the second-most populous country after India, with a population exceeding 1.4 billion, representing 17% of the world's population. China borders fourteen countries by land across an area of 9.6 million square kilometers (3,700,000 sq mi), making it the third-largest country by area. The country is divided into 33 province-level divisions: 22 provinces, 5 autonomous regions, 4 municipalities, and 2 semi-autonomous special administrative regions. Beijing is the capital, while Shanghai is the most populous city by urban area and largest financial center. The first humans in China arrived during the Paleolithic era. By the 2nd millennium BCE dynastic states had emerged in the Yellow River basin. The 8th–3rd centuries BCE saw a breakdown in the authority of the Zhou dynasty, accompanied by the emergence of administrative and military techniques, literature and philosophy. In 221 BCE, China was unified under an emperor, ushering in two millennia of imperial rule. Chinese achievements include the invention of gunpowder, paper, printing and the compass, the establishment of the Silk Road, and the building of the Great Wall.