Medieval machines and inventions, such as the treadwheel crane, became indispensable during construction, and techniques of building wooden scaffolding were improved upon from Antiquity. When building in stone a prominent concern of medieval builders was to have quarries close at hand. There are examples of some castles where stone was quarried on site, such as Chinon, Château de Coucy and Château Gaillard. When it was built in 992 in France the stone tower at Château de Langeais was high, wide, and long with walls averaging . The walls contain of stone and have a total surface (both inside and out) of . The tower is estimated to have taken 83,000 average working days to complete, most of which was unskilled labour.