The physical difficulties encountered, however, were quite real. Without a plentiful and convenient supply of some suitable writing medium, any very extended development of the arithmetic processes was bound to be hampered. It must be remembered that our common machine-made pupl paper is less than a hundred years old. The older rag paper was made by hand, was consequently expensive and scarce, and, even at that, was not introduced into Europe until the twlfth century, although it is likely that the Chinese knew how to make it a thousand years before.