ancient device for grinding grain. The saddle quern, consisting simply of a flat stone bed and a rounded stone to be operated manually against it, dates from Neolithic times (before 5600 BC). The true quern, a heavy device worked by slave or animal power, appeared by Roman times. Cato the Elder describes a 2nd-century-BC rotary quern consisting of a concave lower stone and a convex upper, turned by a pair of asses. Many such large querns were found in the ruins of Pompeii. The upper stone was set on a spindle that fitted into the lower. The ground grain passed down through holes in the lower stone.