Saint Clement (often referred to as either the first, second, third, or fourth pope) tells us about the existence of the "500-year-old phoenix bird" in his First Epistle. The epistle is important as it is gathering up for papal authority.
Quote:Let us consider that wonderful sign of the resurrection which takes place in eastern lands, that is, in Arabia and the countries round about. There is a certain bird which is called a phœnix. This is the only one of its kind, and lives five hundred years. And when the time of its dissolution draws near that it must die, it builds itself a nest of frankincense, and myrrh, and other spices, into which, when the time is fulfilled, it enters and dies. But as the flesh decays a certain kind of worm is produced, which, being nourished by the juices of the dead bird, brings forth feathers. Then, when it has acquired strength, it takes up that nest in which are the bones of its parent, and bearing these it passes from the land of Arabia into Egypt, to the city called Heliopolis. And, in open day, flying in the sight of all men, it places them on the altar of the sun, and having done this, hastens back to its former abode. The priests then inspect the registers of the dates, and find that it has returned exactly as the five hundredth year was completed.
The Epistle of St Clement to the Corinthians
teachings of the Bible are so muddled and self-contradictory that it was possible for Christians to happily burn heretics alive for five long centuries. It was even possible for the most venerated patriarchs of the Church, like St. Augustine and St. Thomas Aquinas, to conclude that heretics should be tortured (Augustine) or killed outright (Aquinas). Martin Luther and John Calvin advocated the wholesale murder of heretics, apostates, Jews, and witches. - Sam Harris, "Letter To A Christian Nation"