It is difficult to tell how smelting was discovered, although the making and use of bronze implements is an indication of the first process of smelting ores and combining metals. When tin was first discovered is not known, but we know that bronze {102} implements made from an alloy of copper, tin, and usually other metals were used by the Greeks and other Aryan peoples in the early historic period, about six thousand years ago. In Egypt and Babylon many of the inscriptions make mention of the use of iron as well as bronze, although the extended use of the former must have come about some time after the latter. At first all war instruments were stone and wood and later bronze, which were largely replaced by iron at a still later period. The making of spears, swords, pikes, battle-axes, and other implements of war had much to do with the development of ingenious work in metals. The final perfection of metal work could only be attained by the manufacture of finely treated steel. Probably the tempering of steel began at the time iron came prominently into use. Other metals, such as silver, quicksilver, gold, and lead, came into common use in the early stages of civilization, all of which added greatly to the arts and industries. Nearly all of the metals were used for money at various times. The aids to trade and commerce which these metals gave on account of their universal use and constant measure of value cannot be overestimated. _Transportation as a Means of Economic Development_.--Early methods of carrying goods from one place to another were on the backs of human beings. Many devices were made for economy of service and strength in carrying. Bands over the shoulders and over the head were devised for the purpose of securing the pack on the back. An Indian woman of the Southwest would carry a large basket, or _keiho_, on her back, secured by a band around her head for the support of the load. A Pueblo woman will carry a large bowl filled with water or other material, on the top of her head, balancing it by walking erect. Indeed, in more recent times washerwomen in Europe, and of the colored race in America, carry baskets of clothes and pails of water on their heads. The whole process of the development of transportation came about through invention to be relieved from this bodily service. {103}