museo-vaticano-chiaramonti-1370
For a good photogrpah on wikimedia commons see http://commons.wikimedia.org/wiki/File:Mill-stone_Chiaramonti_Inv1370_n2.jpg . This model made from a combination of personal and open licensed images. To see a model of an actual mill, go to http://p3d.in/w0SZO .