<human>:  When did the ancient Egyptians start to worship the sun god Ra?
<bot>: The ancient Egyptians worshipped the sun god Ra from the earliest days of the civilization. They built the pyramids to honor Ra and his journey through the underworld. The pyramids were also built as tombs for the pharaohs, who believed they would follow Ra into the afterlife. The Egyptians also believed Ra had created the world, and he was the god of the sky and the source of light.