Mills are one of the most important buildings in the Dark Age as they are drop places for food. They must be placed near a rich source of food like Berry Bushes and Deer. Building a Mill next to Wild Boars or herdables is not necessary, as these units can be lured/herded to the Town Center or an already built Mill. In later stages of the game, the Mill becomes less important, as usually all freely available food is gathered and enough Town Centers are built to produce enough food with Farms next to them.