“In this city of Cambalú is the mint of the grand khan, who may truly be said to possess the secret of the alchemists, as he has the art of producing money by the following process. He causes the bark to be stripped from those mulberry-trees the leaves of which are used for producing silk-worms, and takes from it that thin inner rind which lies between the coarser bark and the wood of the tree. This being steeped, and afterwards pounded in a mortar, until reduced to a pulp, is made into paper, resembling that which is manufactured from cotton, but quite black. When ready for use , he has it cut into pieces of money of different sizes, nearly square but somewhat longer than they are wide.”

The Travels of Marco Polo
translated by W. Marsden, revised T. Wright, edited Peter Harris