The Phoenix is a legendary bird which was reported initially by Herodotus, but was later written about by Pliny, Ovid and Tacitus, as well as being captured in a poem by the early Christian writer, Lactantius. Many of the details vary, but the essential story line is that it was a crimson, gold and purple bird with sweeping tail and jeweled eyes. It lived in a distant garden of flowers and crystal springs. When it grew old and began to tire, it built a nest of spices, herbs and resin in the top of a date palm. Raising its wings to the newly risen Sun on the horizon at dawn, the Phoenix is consumed in the flames of its own funeral pyre. It is then burned to ashes, but later, in the starlight, a young phoenix forms in the ashes of its parent. The reborn bird rises with the rising sun and again spreads its wings to greet the day. It flies high above the pyre, with the strength and enthusiasm of its youth, and is followed by all the birds of the air. These two birds, parent and offspring, are one and the same. There is only one phoenix in the entire world, and it lives on forever, throughout eternity, after repeating this ritual at a specific interval every so many years (myths vary as to precisely how long).
Many of these writers mention that the bird is sacred to the Sun, but it's associations with death and rebirth are obvious, and hence it's identification with Pluto astrologically. For this same reason, Christians identified it with the reborn Christ.
The following is Ovid's report on the Phoenix from his Metamorphosis:
And Nature, always making old things new,
Proves nothing dies within the universe,
But takes another being in new forms.
What is called birth is change from what we were,
And death the shape of being left behind.
Though all things melt or grow from here to there,
Yet the same balance of the world remains.
"How many creatures walking upon this earth
Have their first being in another form?
Yet one exists that is itself forever,
Reborn in ageless likeness through the years.
It is that bird Assyrians call the Phoenix,
Nor does he eat the common seeds and grasses,
But drinks the juice of rare, sweet-burning herbs.
When he has done five hundred years of living
He winds his nest high up a swaying palm
And delicate dainty claws prepare his bed
Of bark and spices, myrrh and cinnamon
And dies while incense lifts his soul away.
Then from his breast- or so the legend runs-
A little Phoenix rises over him,
To live, they say, the next five hundred years.
When he is old enough in hardihood.
He lifts his crib (which is his father's tomb)
Midair above the tall palm wavering there
And journeys toward the city of the Sun,
Where in Sun's temple shires the Phoenix' nest."