pp. 122-23    "You must know that he has money made for him by the following process, out of the bark of trees--to be precise, from mulberry trees (the same whose leaves furnish food for silk-worms). The fine bast between between the bark and the wood of the tree is stripped off. Then it is crumbled and pounded and flattened out with the aid of glue into sheets like sheets of cotton paper, which are all black. When made, they are cut up into rectangles of various sizes, longer than they are broad. The smallest is worth half a small tornesel; the next an entire such tornesel; the next half a silver groat; the next an entire silver groat, equal in value to a silver groat of Venice and there are others equivalent to two, five, and ten groats and one, three, and as many as ten gold bezants. And all these papers are sealed with the seal of the Great Khan. The procedure of issues is as formal and as authoritative as if they were made of pure gold or silver. On each piece of money several specially appointed officials write their names, each setting his own stamp. When it is completed in due form, the chief of the officials deputed by the Khan dips in cinnabar the deal of bull assigned to him and stamps it on the top of the piece of money so that the shape of the seal in vermilion remains impressed upon it. And then the money is authentic. And if anyone were to forge it, he would suffer the extreme penalty.
    "Of this money the Khan has such a quantity made that with it he could buy all the treasure in the world. With this currency he orders all payments to be made throughout every province and kingdom and region of his empire. And no one dares refuse it on pain of losing his life. And I assure you that all the people and populations who are subject to his rule are perfectly willing to accept these papers in payment, since wherever they go they pay in the same currency, whether for goods or for pearls or precious stones or gold of silver. With these pieces of paper they can buy anything and pay for anything. And I can tell you that the papers that reckon as ten bezants do not weigh one."

The Travels of Marco Polo. Ronald Latham, trans.