The introduction of iron occurred in comparatively recent times. At first it was a scarce, and therefore a very precious, metal. The Egyptians seem to have made little use of iron before 1500 B.C. They called it "the metal of heaven," as if they obtained it from meteorites. In the Greek Homeric poems, composed about 900 B.C. or later, we find iron considered so valuable that a lump of it is one of the chief prizes at athletic games. In the first five books of the Bible iron is mentioned only thirteen times, though copper and bronze are referred to forty-four times. Iron is more difficult to work than either copper or bronze, but it is vastly superior to those metals in hardness and durability. Hence it gradually displaced them throughout the greater part of the Old World. [2] FIRST STEPS TOWARD CIVILIZATION During the prehistoric period early man came to be widely scattered throughout the world. Here and there, slowly, and with utmost difficulty, he began to take the first steps toward civilization. The tools and weapons which he left behind him afford some evidence of his advance. We may now single out some of his other great achievements and follow their development to the dawn of history. 3. DOMESTICATION OF ANIMALS AND PLANTS HUNTING AND FISHING STAGE Prehistoric man lived at first chiefly on wild berries, nuts, roots, and herbs. As his implements improved and his skill increased, he became hunter, trapper, and fisher. A tribe of hunters, however, requires an extensive territory and a constant supply of game. When the wild animals are all killed or seriously reduced in number, privation and hardship result. It was a forward step, therefore, when man began to tame animals as well as to kill them. DOMESTICATION OF THE DOG The dog was man's first conquest over the animal kingdom. As early as the Age of Metals various breeds appear, such as deerhounds, sheep dogs, and mastiffs. The dog soon showed how useful he could be. He tracked game, guarded the camp, and later, in the pastoral stage, protected flocks and herds against their enemies. THE COW The cow also was domesticated at a remote period. No other animal has been more useful to mankind. The cow's flesh and milk supply food: the skin provides clothing; the sinews, bones, and horns yield materials for implements. The ox was early trained to bear the yoke and draw the plow, as we may learn from ancient Egyptian paintings. [3] Cattle have also been commonly used as a kind of money. The early Greeks, whose wealth consisted chiefly of their herds, priced a slave at twenty oxen, a suit of armor at one hundred oxen, and so on. The early Romans reckoned values in cattle (one ox being equivalent to ten sheep). Our English word "pecuniary" goes back to the Latin _pecus_, or "herd" of cattle. [Illustration: EARLY ROMAN BAR MONEY A bar of copper marked with the figure of a bull. Dates from the fourth century B.C.] THE HORSE