We briefly surveyed the ideas and techniques of the early human beings, and traced the roots of science in the primitive culture. You also read about the emergence and growth of science in the ancient world, in the historical epoch known as the Bronze Age. Now, we turn our attention to an equally important period in the history of science, known a:; the Iron Age. From about the fifteenth century B.C., we find that civilisation was no longer limited to a few river basins but had spread to the major cultivable areas of Asia, northern Africa and Europe. The spread of civilisation was aided by the discovery and use of a new metal, iron, which led to this period being called as the Iron Age. The Iron Age did not bring about any remarkable technical advances, such as in the Bronze Age. However, the availability of a cheap and abundant metal led to widespread changes as this civilisation spread far and wide. It also affected the relations between various social classes. , We have already read that the Bronze Age river valley civilisations were decaying due to many problems of stagnating economy and culture. Their decline was hastened by the constant incursions and raids of barbarian clans. The nomadic barbarians were pastoral people who had learnt to use iron. They had great mobility as they had tamed wild horses for travel, and carried their food alongwith them. They ran through the decaying civilisations, picking up local techniques as it suited them. The devastation left in their wake was often irreparable for the people they had over-run. The barbarians spread far and wide in the world, giving rise to civilisations that were less peaceful, even less developed, but more flexible to change. In this unit, we shall study about the developments in science and technology in the Indian and Greek civilisations of the Iron Age. In the next unit, we shall take up the study of one of the most fruitful periods of scientific.developments in India, which saw tremendous advances in the areas of astronomy, mathematics and technology.