The Assyrians fell at last to one of their subject peoples, the Chaldeans, who rebuilt Babylon and won a lustrous place in history for their intellectual achievements in astronomy, medicine, and mathematics. They used a base-12 system (as opposed to our base-10 system) and were pioneers in the measurement and division of time, which is why the year has twelve months, the hour has sixty minutes (five times twelve), and the minute has sixty seconds. They were terrific urban planners and architects—it was a Chaldean king who built those Hanging Gardens of Babylon, which the ancients ranked among the seven wonders of the world.