The Tang Dynasty was an imperial dynasty of China that lasted from 618 to 907. It was founded by the Li family, who seized power during the decline and collapse of the Sui Empire. The Tang Dynasty, with its capital at Chang'an, the most populous city in the world at the time, is regarded by historians as a high point in Chinese civilization—equal to or surpassing that of the earlier Han Dynasty—as well as a golden age of cosmopolitan culture. In Chinese history, the Tang Dynasty was largely a period of progress and stability, except during the An Shi Rebellion and the decline of central authority in the latter half of the dynasty. Like the previous Sui Dynasty, the Tang Dynasty maintained a civil service system by drafting officials through standardized examinations and recommendations to office. Two of China's most famous historical poets, Du Fu and Li Bai, belonged to this age, as well as the poets Meng Haoran, Du Mu, and Bai Juyi. Many famous visual artists lived during this era, such as the renowned painters Han Gan, Zhang Xuan, and Zhou Fang. There was a rich variety of historical literature compiled by scholars, as well as encyclopedias and books on geography. There were many notable innovations during the dynasty, including the development of woodblock printing, the escapement mechanism in horology, the government compilations of materia medicas, and improvements in cartography.