Civilizations first developed in East and South Asia in the vicinity of great river systems. When irrigated by the massive spring floods of the Yellow River, the rich soil of the North China plain proved a superb basis for what has been the largest and most enduring civilization in human history. Civilization first developed in the Indus River valley in present-day Pakistan in the middle of the 3d millennium B.C., more than a thousand years earlier than it did in China. In fact, the civilization of the Indus valley, usually called Harappan after its chief city, rivals Sumer and Egypt as humanity's oldest. But like Sumer and its successor civilizations in the Middle East, Harappan civilization was unable to survive natural catastrophes and nomadic invasions. In contrast to the civilization of the Shang rulers in China around 1500 B.C., Harappa vanished from history. Until the mid-19th century it was "lost" or forgotten, even by the peoples who lived in the vicinity of its sand-covered ruins. Important elements of Harappan society were transmitted to later civilizations in the Indian subcontinent. But unlike the Shang kingdom, Harappa did not survive to be the core and geographical center from which a unified and continuous civilization developed like that found in China. The difference in the fate of these two great civilizations provides one of the key questions in dealing with the history of civilized societies: What factors permitted some civilizations to endure for millennia while others rose and fell within a few centuries?

Between about 1500 and 1000 B.C., as the great cities of the Indus region crumbled into ruins, nomadic Aryan invaders from central Asia moved into the fertile Indus plains and pushed into the Ganges River valleys to the east. It took these unruly, warlike peoples many centuries to build a civilization that rivaled that of the Harappans. The Aryans concentrated on assaulting Harappan settlements and different Aryan tribal groups. As peoples who depended primarily on great herds of cattle to provide their subsistence, they had little use for the great irrigation works and advanced agricultural technology of the Indus valley peoples. Though they conserved some Harappan beliefs and symbols, the Aryan invaders did little to restore or replace the great cities and engineering systems of the peoples they had supplanted.

Eventually, however, many of the Aryan groups began to settle down, and increasingly they relied on farming to support their communities. By about 700 B.C., their priests had begun to orally record the sacred hymns and ritual incantations that had long been central to Aryan culture. In the following centuries, strong warrior leaders built tribunal units into larger kingdoms. The emergence of priestly and warrior elites signaled the beginning of a new pattern of civilization in South Asia. By the 6th century B.C., the renewal of civilized life in India was marked by the emergence of great world religions, such as Hinduism and Buddhism, and a renewal of trade, urban life, and splendid artistic and architectural achievements.

Great torrents of water from the world's highest mountain range, the Himalayas, carved out the vast Indus River system that was to nurture the first civilization in the Indian subcontinent. As the rapidly running mountain streams reached the plains of the Indus valley, they branched out into seven great rivers, of which five remain today. These rivers in turn converge midway down the valley to form the Indus River, which runs for hundreds of miles to the southwest and empties into the Arabian Sea. The streams that flow from high in the Himalayas are fed by monsoon rains. Rain clouds are carried from The seas surrounding the Indian subcontinent by monsoons seasonal winds across the lowlands to the mountains where, cooled and trapped, they release their life-giving waters. These "summer" or wet monsoons, which blow toward central Asia from the sea, are also a critical source of moisture for the Plains and valleys they cross before they reach the mountain barriers. The streams from the mountains also carry prodigious amounts of rich soil to these plains, constantly enlarging them and giving them the potential for extensive cultivation and dense human habitation. The Indus is only one of many river systems in the Indian subcontinent formed by melting snow and monsoon rains, but it was the first to nurture a civilization.

The lower Indus plains were a very different place in the 3d millennium B.C. than they are today. Most of the region is now arid and desolate, crisscrossed by dried-up riverbeds and virtually devoid of forests. In Harappan times, it was green and heavily forested. Game animals and pasturage for domesticated animals were plentiful. Long before the first settlements associated with the Harappan complex appeared, the plains were dotted with the settlements of sedentary agriculturists. By at least 3000 B.C., these pre-Harappan peoples cultivated wheat and barley, and had developed sophisticated agricultural implements and cropping techniques. The pre-Harappan peoples knew how to make bronze weapons, tools, and mirrors, and they had mastered the art of pottery making. Recurring motifs, such as bulls and long-horned cattle on elaborately decorated bowls and storage urns, suggest links to early agricultural communities in the Middle East, while fish designs indicate a preoccupation with what was probably a major source of food. The long-horned bull was a central image in the Harappan culture and remains important in Indian iconography, the art of pictorial representation. Pre-Harappan peoples in the Indus valley also carved large numbers of small figurines of women. These statuettes differ from those found in many other early cultures in the detailed attention given to hairstyles and Jewelry. Early village sites also contained tiny carts with clay wheels that may be the earliest children's toys yet discovered.

In the late 1850s, the British were directing the building of railway lines through the Indus valley. In need of bricks for the railway bed, the engineers allowed the construction workers to plunder those bricks found in the dirt mounds of long-abandoned cities in the valley. A British general named Cunningham, who would later be the head of the Indian Archeological Survey, visited one of these sites in 1856. While there, he was given a number of artifacts including several soapstone seals imprinted with various Carvings, including the figure of a bull and what were apparently letters in a script. Cunningham was convinced that the artifacts were of ancient origin and was intrigued by the strange script, which bore little resemblance to that of any of the languages then in use in various parts of India. As head of the Archeological survey, Cunningham took steps to ensure the full-scale excavation of what came to be recognized as one of the earliest and most mysterious of all human civilizations.