Egypt's Old Kingdom flourished on the flood-enriched banks of the River Nile. It was an era of prosperity, relative stability, and strong centralized rule. During this period, the pyramids were built and Egyptian society worshipped their mighty kings, or pharaohs, as 'gods on Earth'. Old Kingdom society was tightly controlled by the powerful pharaoh. Central to life, politics, and religion, which were all closely combined, was the idea that the pharaoh was a semi-divine figure who acted as mediator between the gods and his people. The pharaoh not only oversaw elaborate religious rituals but also headed a vast, highly organized political and administrative bureaucracy. Pharaohs were believed to be earthly representations of the gods and were the upholders of a justice system that aimed to reflect the cosmic order. A pharaoh was also the figure who worked with the gods to ensure that the Nile brought silt-rich annual floods each year, maintaining the Nile valley fertile enough to support the country. Though Egyptians did seem to realize he was a flesh-and-blood human, they stood in awe of the sacred power of the pharaoh.