From the earliest settlements along the Indus River, the Dravidians and later the Aryans spread their settlements deep into the sub-continent. Protected by geographic barriers, the valley inhabitants had limited contact the outside world. Farmers cultivated cotton and processed it into cloth which became a valuable trade commodity. Their cities were well planned with shops, granaries, extensive sewerage systems and protective walls. Two major religions, Buddhism and Hinduism, developed in India and spread throughout Asia. Art served religion well in India. The artists of the area cut unique Buddhist Temples from rocky cliffs with facades and interiors intricately carved to imitate the wooden constructions of the period. From the earliest simple structures to the ornate and imposing later ones, the Hindu Temples must be appreciated as sculpture as well as architecture. Their paintings, particularly from the Gupta dynasty, are classed as some of the finest in history.