The 4 major early river valley civilizations developed advanced cultures with organized governments, economies, religions, and technologies. The Sumerians in Mesopotamia invented cuneiform writing and the wheel. The Egyptians built the great pyramids and Sphinx, and established hieroglyphic writing. The Indus Valley civilization had well-organized cities of Harappa and Mohenjo-Daro. The Chinese called themselves the Middle Kingdom and invented their writing system with symbols representing ideas. These civilizations contributed irrigation, money, metal tools, architecture, polytheistic religions, and some of the earliest written laws.