The earliest bread was made with grain that had to be ground using a labour-intensive, manual grindstone called a hand quern. Grinding even a small amount of grain was a time-consuming and tedious task that made a very gritty, dense bread that wreaked havoc on people’s teeth. With the advent of grain mills in medieval times, powered by animals, water or wind to grind the grain between two large stones, people could buy flour or take their grain to the mill to be milled into flour in exchange for a fee or portion of their harvest. These mills were usually maintained by a monastery or feudal lords. The Domesday Book lists around 6000 mills in England in 1086.