One of the greatest inventions of the medieval world was the mechanical clock. The difficulty in inventing a mechanical clock was to figure out a way in which a wheel no bigger than a room could turn at the same speed as the Earth, but still be turning more or less continuously. If this could be accomplished, then the wheel became a mini Earth and could tell the time.
Yi Xing, a Buddhist monk, made the first model of a mechanical clock in 725 AD. This clock operated by dripping water that powered a wheel which made one full revolution in 24 hours. An iron and bronze system of wheels and gears made the clock turn. This system caused the chiming of a bell on the hour.