top of the altar, an arch-shaped rammed earth foundation facing the east with 12 slots, each 0.15 to 0.2 m wide and 1.4 m between each other were discovered; standing in the center of the altar and watching through the slots, one can find that most of slots respectively orientate to a given point of the Chongfen Mountain to the east. In a given period in the ancient times, the midwinter sunrise of the winter solstice would have been in the middle of the second eastern slot, the midsummer sunrise of the summer solstice would have been in the middle of the westmost slot, and during the seasons the sun would rise within each of the slots from west to east, marking the passage of time between the winter solstice and the summer solstice. This means these slots shares a similar function of the Thirteen Towers of the Chankillo Observatory, and they might have been intentionally constructed in for astronomical observation of the sunrise on a particular point in a given day, in order to establish the local solar calendar, which is crucial for the practice of agriculture at that time. Necropolis The cemetery of Taosi covered an area of 30,000 square meters (3ha) at its height. The cemetery contained over 1,500 burials. The burials at Taosi were highly stratified (the most stratified of Longshan sites), with burial wealth concentrated in the graves of a few males (nine large graves). The largest graves were placed in separated rooms with murals, had a large cache of grave goods (some with over 200 objects, including jades, copper bells, wooden and crocodile skin musical instruments); middle-size graves featured painted wooden coffins and luxury objects; most of the small graves did not have grave goods. A single bronze bell was also found at a Taosi grave. Emperor Yao connection Several Chinese archaeologists postulate that Taosi was the site where the state of Youtang (有唐) being conquered by Emperor Yao, (traditionally c. 2356–2255 BC) who later instituted Taosi as the capital. In Chinese classic documents Yao Dian (Document of Yao) in Shang Shu (Book of Ancient Time), and Wudibenji (Records for the Five Kings) in Shiji (Historic Records), King Yao assigned astronomic officers to observe celestial phenomena, including time and position of sunrise, sunset, and stars in culmination, in order to systematically establish a solar calendar and a lunar calendar with 366 days a year