And four great beasts came up from the sea - Not at once, but in succession. See the following verses. Their particular form is described in the subsequent verses. The design of mentioning them here, as coming up from, the sea, seems to have been to show that this succession of kingdoms sprang from the agitations and commotions among the nations represented by the heaving ocean. It is not uncommon for the prophets to make use of animals to represent or symbolize kingdoms and nations - usually by some animal which was in a manner peculiar to the land that was symbolized, or which abounded there. Thus in Isaiah 27:1, leviathan, or the dragon, or crocodile, is used to represent Babylon. See the note at that passage. In Ezekiel 29:3-5, the dragon or the crocodile of the Nile is put for Pharaoh; in Ezekiel 32:2, Pharaoh is compared to a young lion, and to a whale in the seas. In Psalms 74:13-14, the kingdom of Egypt is compared to the dragon and the leviathan.
So on ancient coins, animals are often used as emblems of kingdoms, as it may be added, the lion and the unicorn represent Great Britain now, and the eagle the United States. It is well remarked by Lengerke (in loc.), that when the prophets design to represent kingdoms that are made up of other kingdoms, or that are combined by being brought by conquest under the power of others, they do this, not by any single animal as actually found in nature, but by monsters - fabulous beings that are compounded of others, in which the peculiar qualities of different animals are brought together - as in the case of the lion with eagle’s wings. Thus in Revelation 13:1, the Romish power is represented by a beast coming out of the sea, having seven heads and ten horns, Compare it. Ezra (Apocry.) 11:1, where an eagle is represented as coming from the sea with twelve feathered wings and three heads. As an illustration of the attempts made in the apocryphal writings to imitate the prophets, the whole of chapter 11 and chapter 12 of the second book of Ezra may be referred to.
Diverse one from another - Though they all came up from the same abyss, yet they differed from each other - denoting, doubtless, that though the successive kingdoms referred to would all rise out of the nations represented by the agitated sea, yet that in important respects they would differ from each other.