Baking also evolved over ancient Egypt's long history. Excavation of a bakery dating to the Old Kingdom at Giza evidences that heavy pottery bread molds were set in rows on a bed of embers to bake the dough placed within them. By the Middle Kingdom, square hearths were used, and the Next, the the whole grain was milled into flour, usually using a flat grinding stone known as a Next, the the whole grain was milled into flour, usually using a flat grinding stone known as a saddle quern. From Neolithic times through the Old Kingdom, these grinding stones were placed on the floor, which made the process difficult.