If the utility of an invention were somehow derived from the genius of its inventor, it would be pardonable that so many sources trace the idea for the ball bearing to a 1497 drawing by Leonardo da Vinci. But good ideas, like useful evolutionary traits, tend to emerge more than once, in diverse times and places, and the idea of arranging for parts to roll against one another instead of sliding or slipping is very old indeed. The Egyptians already had the basic idea when they moved great blocks of stone on cylindrical rollers. Similar ideas occurred to the builders of Stonehenge as early as 1800 B.C. and to the craftsmen who constructed the cylindrical-shaped bearings on the wheel hubsof wagons around 100 B.C. (On these wagons the axle turned with the wheels, so the bearings enabled the axle to roll against the wagon chassis.)