Querns are hand-operated mills, in which grain (mainly wheat, barley and rye) was ground to produce flour. They are common finds on all types of Roman sites, showing that most of the flour used to make bread in forts, farms, and towns was ground on a small scale at the place it was used.
These were used by people in Iron Age England before the Romans arrived and continued in use during the Roman period. Typically they measure up to about 30cm in diameter and consist of a rotating distinctive heavier dome shaped upper stone on top of a stationary lower stone. Grain was fed into a hole in the centre of the upper stone, which was turned with a wooden handle fixed into the side of the stone.
There were regional variations in style and design. Initially the military imported querns made of volcanic lava from Mayen and other places in the Eifel Mountains in Germany, west of Koblenz on the Rivers Rhine and Mosel. Later on regional variations were made with local hard stones such as Millstone Grit from Derbyshire. Querns would have been set onto a table or used on the ground. The resulting flour would have needed sieving before using to make bread, not least of all to remove grit from the stones.