Re (or Ra) was the Egyptian Sun god. The early Egyptians believed that he created the world, and this is why the rising Sun was the symbol of creation. The daily cycle of the Sun moving across the sky represented creation and renewal.
Re was seen as a mirror image of the pharaoh, one ruling the universe, the other ruling the Earth. Horus and Re were merged in the symbol of a winged Sun disk.
In the 5th Dynasty kings built pyramids in line with the rising and setting Sun.
