Sentence:  Ancient nomads, wishing to ward off the evening chill and enjoy a meal around a campfire, had to collect wood and then spend time and effort coaxing the heat of friction out from between sticks to kindle a flame. With more settled people, animals were harnessed to <WSD>capstans</WSD> or caged in treadmills to turn grist into meal. 
Meaning of the word marked with <WSD> tags:  A vertical cylindrical machine that revolves on a spindle, used to apply force to ropes, cables, etc. It is typically surmounted by a drumhead with sockets for levers used to turn it.