To make wheat flour the wheat must be ground by one means or another. The evolution of grinding and milling techniques began with the earliest known pestle and mortar, dating from about 10000 bc; this came from the Azilian culture of S. France, where it was used to grind pigments. No doubt pestles and mortars were subsequently used for grains, but the result they produce, although adequate for a gruel or pottage, does not really produce flour for bread.
In most places where a series of early food-grinding implements has been found, development can be seen to have proceeded in one of two ways. One was the larger mortar worked by two or more people pounding alternately with long-handled pestles, as is still seen in Africa. This is quicker, but does not give a finer grind. The other is a device in which the top stone, or pestle, rubs against the lower stone, or mortar, with a shearing effect on the grain which can produce flour as we know it. A large surface area is needed for efficiency, so the original bowl shape of the mortar is opened out into a flat form, generally at first with raised edges. This is set in front of the kneeling operator, sloping away from the body. A smaller, flat-bottomed stone is rubbed back and forth across the grain. The flour collects at the far end, where there is often a hollow.