The civilisation of ancient Greece was nurtured within city walls. In fact, all the modern civilisations have their cradles of brick and mortar. These walls leave their mark deep in the minds of men. They set up a principle of "divide and rule" in our mental outlook, which begets in us a habit of securing all our conquests by fortifying them and separating them from one another. We divide nation and nation, knowledge and knowledge, man and nature. It breeds in us a strong suspicion of whatever is beyond the barriers we have built, and everything has to fight hard for its entrance into our recognition. When the first Aryan invaders appeared in India it was a vast land of forests, and the newcomers rapidly took advantage of them. These forests afforded them shelter from the fierce heat of the sun and the ravages of tropical storms, pastures for cattle, fuel for sacrificial fire, and materials for building cottages. And the different Aryan clans with their patriarchal heads settled in the different forest tracts which had some special advantage of natural protection, and food and water in plenty. Thus in India it was in the forests that our civilisation had its birth, and it took a distinct character from this origin and environment. It was surrounded by the vast life of nature, was fed and clothed by her, and had the closest and most constant intercourse with her varying aspects. Such a life, it may be thought, tends to have the effect of dulling human intelligence and dwarfing the incentives to progress by lowering the standards of existence. But in ancient India we find that the circumstances of forest life did not overcome man's mind, and did not enfeeble the current of his energies, but only gave to it a particular direction. Having been in constant contact with the living growth of nature, his mind was free from the desire to extend his dominion by erecting boundary walls around his acquisitions. His aim was not to acquire but to realise, to enlarge his consciousness by growing with and growing into his surroundings. He felt that truth is all-comprehensive, that there is no such thing as absolute isolation in existence, and the only way of attaining truth is through the interpenetration of our being into all objects. To realise this great harmony between man's spirit and the spirit of the world was the endeavour of the forest-dwelling sages of ancient India.