 Several remains of crossbows have been found among the soldiers of the Terracotta Army in the tomb of Qin Shi Huang.The Eastern Han dynasty scholar and astronomer Zhang Heng (78–139 AD) invented the first water-powered rotating armillary sphere (the first armillary sphere having been invented by the Greek Eratosthenes), and catalogued 2,500 stars and over 100 constellations.In 132, he invented the first seismological detector, called the ""Houfeng Didong Yi"" ("Instrument for inquiring into the wind and the shaking of the earth").