History of the world
Whether in prehistoric or historic times, people always needed to be near reliable sources of potable water. Settlements developed on river banks as early as 3000 BCE in Mesopotamia, on the banks of Egypt's Nile River, in the Indus River valley, and along China's rivers. As farming developed, grain agriculture became more sophisticated and prompted a division of labour to store food between growing seasons. Labour divisions led to the rise of a leisured upper class and the development of cities, which provided the foundation for civilization. The growing complexity of human societies necessitated systems of accounting and writing.
Harappa
The Harappan Civilization has its earliest roots in cultures such as that of Mehrgarh, approximately 6000 BC. The two greatest cities, Mohenjo-daro and Harappa, emerged circa 2600 BC along the Indus River valley in Punjab and Sindh. The civilization, with a possible writing system, urban centers, and diversified social and economic system, was rediscovered in the 1920s also after excavations at Mohenjo-daro in Sindh near Larkana, and Harappa, in west Punjab south of Lahore. A number of other sites stretching from the Himalayan foothills in east Punjab, India in the north, to Gujarat in the south and east, and to Pakistani Balochistan in the west have also been discovered and studied. Although the archaeological site at Harappa was damaged in 1857 when engineers constructing the Lahore-Multan railroad (as part of the Sind and Punjab Railway), used brick from the Harappa ruins for track ballast, an abundance of artifacts have nevertheless been found. The bricks discovered were made of red sand, clay, stones and were baked at very high temperature. As early as 1826 Harappa, located in west Punjab, attracted the attention of a British officer in India, who gets credit for preliminary excavations in Harappa.