The Pompeian mill shows that as early as the first century the Romans ground their grain by animal power. Indeed about this time a still greater change was made in the method of grinding grain. When Julius Cæsar flourished (50 B. C.) men began to harness the power of running water and make it turn their mills (Fig. 11). From Figure 12 we may easily learn how this was done. The running water turns the wheel and in doing so turns the upper millstone. A hopper is suspended from the roof by ropes. Through this the grain passes into the mill. Here was a great saving in human labor and a great advancement in mill making. A Roman writer of Cæsar's time appreciating how great a blessing was the invention of the water-mill exclaimed: Ye maids who toiled so faithful at the mill Now cease from work and from these toils be still; Sleep now till dawn and let the birds with glee Sing to the ruddy morn, on bush and tree; For what your hands performed so long, so true, Ceres[15] has charged the water-nymphs to do; They come, the limpid sisters, to her call, And on the wheel with dashing fury fall; Impel the axle with a whirling sound And make the massive millstone reel around And bring the floury heap luxuriant to the ground. Nothing can be simpler than the water-mill described above; it was the old mill of the upper and nether millstones, the old hand mill turned by water. That was all. Yet, as simple as it was, many centuries passed after its invention before a new principle in flour making was discovered. There were inventions for lowering and raising the stone so as to grind finer or coarser as might be desired, and there were improvements in the kind of water wheels employed, and better methods of sifting the flour from the bran were discovered from time to time, but the water-mill invented in the time of Julius Cæsar remained practically unchanged until the early part of the nineteenth century, when the last step in the development of the mill was taken.[16] [Illustration: FIG. 13.--AN EARLY FLOUR ROLLER-MILL.]