India's extraordinary history is intimately tied to its geography. A meeting ground between the East and the West, it has always been an invader's paradise, while at the same time its natural isolation and magnetic religions allowed it to adapt to and absorb many of the peoples who penetrated its mountain passes. No matter how many Persians, Greeks, Chinese nomads, Arabs, Portuguese, British and other raiders had their way with the land, local Hindu kingdoms invariably survived their depredations, living out their own sagas of conquest and collapse. All the while, these local dynasties built upon the roots of a culture well established since the time of the first invaders, the Aryans. In short, India has always been simply too big, too complicated, and too culturally subtle to let any one empire dominate it for long.
The civilization that laid the bricks, one of the world's oldest, was known as the Indus. They had a written language and were highly sophisticated. Dating back to 3000 BC, they originated in the south and moved north, building complex, mathematically-planned cities. Some of these towns were almost three miles in diameter and contained as many as 30,000 residents. These ancient municipalities had granaries, citadels, and even household toilets. In Mohenjodaro, a mile-long canal connected the city to the sea, and trading ships sailed as far as Mesopotamia. At its height, the Indus civilization extended over half a million square miles across the Indus river valley, and though it existed at the same time as the ancient civilizations of Egypt and Sumer, it far outlasted them.