The ancient Egyptians had a tale of how the earth emerged—one of their many tales of how our world came to be.
They envisioned a great watery chaos. And in the middle of the swirling waters appeared a little earthen mound, called the Benben. And standing on top of that mound was the Benu bird (or Bennu bird), the Gray Heron. And the earthen mound grew and grew, larger and larger, until it became the wide earth that we walk on every day.
This tale seemed strange to me until the other day, when I was on the Nile ferry. A clump of weed was floating down the river. And an egret was standing tall and serene on that rapidly-floating clump of weed.
Now it all made sense. When the Nile flooded, great clumps of mud with vegetation floated down the river, with long-legged avian passengers standing on them. This flood brought the rich black soil which made possible the harvest, without which life would be impossible.
So the Benu bird was a symbol of life born in the flood-waters.
But the fire of the sun is essential for life—as essential as water. So the ancient Egyptians also believed that the Benu bird was born in the flames of a burning tree in Heliopolis, the city of the sun, near Memphis.
The ancient Greeks adopted this Gray Heron as the Phoenix, born in flame. Herodotus reported that the Phoenix lays an egg in the flames, once every five hundred years, and the new bird hatches from this fire.
The Sothic cycle is an ancient-Egyptian cosmological pattern that repeats roughly every 1500 years (or three times five hundred years). The ancient-Egyptian priests in Heliopolis may have used the legend of the fiery Benu bird to express their knowledge of the Sothic cycle or of some other cosmological cycle. The tale was a kind of code, revealing to the inquisitive Greek stranger the fact that they possessed this knowledge, without revealing too much of the knowledge itself.
So there we have the opposites, flood and fire, united in the paradoxical tale of the Benu bird or Phoenix, symbol of life.
[Wikipedia has an article about the Bennu bird. We have linked to their really cool picture. wh
Wikipedia also has a comprehensive article on the Sothic Cycle.
Also an article about the Phoenix, including the relevant quote from Herodotus.]