Grain agriculture, with its need to store food between growing seasons, enabled the division of labor, the rise of a leisured upper class, and the development of cities and with them civilization. The growing complexity of human societies necessitated systems of accounting, which led to writing. Civilizations developed on the banks of lakes and rivers. By 3000 BCE, they had arisen in the Middle East's Mesopotamia, on the banks of Egypt's River Nile, and in the Indus River valley. Similar civilizations probably developed along major rivers in China, but the archaeological evidence for extensive urban construction is less conclusive.