One Rule of Interpretation of Symbolism, since we are dealing with symbols here, is that if the interpretation of the symbol is given in the Scriptures, then that remains the interpretation unless God says it is otherwise. So we are not left to our imagination to interpret the symbols, rather it is by revelation, and that revelation is one and the same.
All the prophets of the Old and New Testaments saw different things, just as the Gospel writers saw different things, but it was the same scene, just as Matthew, Mark and Luke comment on different attributes of the same healing that Christ performed. They each had a different seat in the audience, with a different viewpoint, but the same revelation. Each prophet had a different seat in time, and saw various attributes about God and His Workings, but they are the same workings, even though each prophet has a different take on them, depending when he lived and what the issues of his time were.
Daniel in Chapter 2 sees the "Bronze" as representitive of the Greek Kingdom. In Chapter 7 he sees a Beast with Iron(Roman) teeth, and brass(Greek) claws, symbolizing that the Romans copied the Greek laws and made them their own. What's more important is that in Revelations 13:1-2 we see the Beast 'like unto a leopard'-in Daniel 7 the 3rd Beast is a leopard with 4 heads. This means the entire Beast carries the attributes of the Greek Kingdom, even though the Greek Kingdom had long disappeared. Greece or the Greek Empire is the leopard, and brass is it's symbolic representation. The horses are the same as the horses of Revelation; the white horse is conquest, but white is the color of purity-remember the King of Kings and the Lord of Lords rides on a white horse. The red horse is warfare, the black horse is famine and the pale horse is plague and death. These are the Judgements of God visited upon the earth; the riderless ones in Chapter 1 are general judgements because of disobedience to the general counsels of God, the ones with riders/chariots are in specific relation to Israel and the words given by God-specific counsel. I don't know why the 2 mountains of brass; since the Greek Empire had not come into being yet, but since the Greek Empire was given dominion over the whole earth, as stated in Daniel, the 4 heads are not only the 4 generals who divided the rule of Alexander the Great but also the 4 Ordinal Directions this kingdom took.(N,S,E,W) Since East and West have little significance in direction for Israel, although they play great importance for the rest of the world, I believe they could be North and South, since these are the kingdoms that have had the greatest impact on Israel.
Interestingly, in Zech.9:13-14 it says,"When I have bent Judah for me, filled with bow with Ephraim, and raised up thy sons, O Zion, against thy sons, O Greece, and made thee as a sword of a mighty man. And the Lord will be seen over them, and His arrow shall go forth as lightning: and the Lord shall blow the trumpet, and shall go with whirlwinds of the south." This is the scene of the last battle, all the nations(the Antichrist/Beast/leopard kingdom-Spiritual Greece) will attempt to annihilate Israel. The Lord will go forth to battle against them and destroy the Statue of Nebuchadnezzar, and the world system which supports it. This Mountain(the Lord and His Kingdom) will fill the entire earth.