The Nile River was central to ancient Egyptian civilization. It flooded annually, depositing rich soil and enabling the Egyptians to grow crops. The Egyptians lived in a fertile area called the Nile Delta. King Menes united Upper and Lower Egypt around 3100 BC, establishing the Old Kingdom. During this time, pharaohs ruled as god-kings and oversaw the construction of pyramids and other great monuments. The Nile and Egyptian religious beliefs centered around gods like Hapi, Re, and Osiris were also important aspects of Egyptian life.