Ancient Egypt developed along the fertile banks of the Nile River around 4,000 BCE. As the climate changed and became hotter and drier, societies were forced to settle along the river, developing irrigation systems and villages. Around 3100 BCE, King Menes unified Upper and Lower Egypt, establishing it as the first centralized state in Africa. Egyptian civilization went on to develop complex social hierarchies, administrative bureaucracies, specialized labor, extensive trade networks, and sophisticated cultural traditions like hieroglyphic writing and monumental architecture and temples. The legacies of ancient Egyptian society continued to influence Nubia and other neighboring cultures for millennia.