16 Now as to the first beast, he said concerning it, that it was like a lion, and it had the wings of an eagle. For the first beast was the kingdom of Babylon, which was like a lion. For thus Jeremiah wrote saying:— Israel is a wandering sheep. The lions caused them to wander. First the king of Assyria devoured him. And this last was stronger than he, Nebuchadnezzar king of Babylon. So Jeremiah called him a lion. And he said:— He has the wings of an eagle.
For thus it is written that, when Nebuchadnezzar went out to the wilderness with the beasts, he grew hair like (the plumage) of an eagle. And he said:— I saw that its wings were plucked away and it stood upright upon its feet as a man, and a man's heart was given to it. For first, in the vision of the image, he was compared to gold which is more precious than anything which is used in the world. So in the vision of the beasts he is compared to a lion which excels in its might all the beasts.
And again he was compared to an eagle which surpasses every bird. Whatsoever was written about him was fulfilled in him. For the Lord said concerning him:— I have placed a yoke of iron upon the neck of all the nations, and they shall serve the king of Babylon seventy years. And also the beasts of the desert and the birds of heaven have I given to him to serve him. For since the king was like the head of gold, men served him as a king. And when he went out to the wilderness, the beasts served him as a lion.
And when his hair was like (the plumage) of an eagle, the birds of heaven served him as an eagle. But when his heart was lifted up, and he knew not that the power was given to him from heaven, the yoke of iron was broken from the neck of men, and he went forth with the beasts, and instead of the heart of a king there was given him the heart of a lion. And when he was lifted up over the beasts, the heart of a lion was taken away from him, and there was given him the heart of a bird. And when wings grew upon him like those of an eagle, he exalted himself over the birds. And then his wings also were plucked away and there was given to him a humble heart. And when he knew that the Most High has authority in the kingdom of man, to give it to whomsoever He will, then as a man he praised Him.
Source: Demonstrations (New Advent)