Built just south of an earlier Yuan Dynasty observatory, the Beijing Ancient Observatory dates back to 1442, and it served as the center of astronomical research (and much astrological speculation) through the Ming and Qing Dynasties. Today's building stands alone, severed from the ancient Beijing city wall that Mao Zedong ordered destroyed to make way for the Second Ring Road. As a result, the observatory sits amidst a graceless jumble of modern buildings and highway overpasses, cloaked in the near-permanent haze of China's booming capital. Most would agree that the observatory has seen better days, but it still exists as an impressive and fascinating monument to the history of science in China. Records of astronomical observations run from 1442 to 1929, making it the record-holder for the longest period of continuous sky watching. The flat top, 14 meters (46 feet) high, is home to an amazing array of instruments, some originals and others replicas. Among the most interesting are those that were constructed under the direction of Jesuit astronomers residing in Beijing at the invitation of Qing emperors; designed to Western specifications with superficial Chinese ornamentation, the bronze instruments are examples of the first wave of modern-era scientific collaboration between China and the West. There is also a small museum with displays on the role of astronomy throughout China's history, along with beautiful models of the heavens in stone and gold.