Ancient Egypt developed along the fertile banks of the Nile River from around 3900 BCE. Key periods included the Old, Middle, and New Kingdoms. Egyptian civilization was unified by the river for transportation and enriched by annual flooding. The Egyptians built monumental structures like the pyramids and temples from stone using skilled labor. Their highly organized society was led by pharaohs who ruled as divine kings and heads of state and religion. Agriculture, trade, and a rigid social hierarchy supported the population.