Cross reference
Daniel 8:20
20 The sheep which you saw with two horns, they are the kings of Media and Persia.
Daniel 8:3
3 And lifting up my eyes, I saw, there before the stream, a male sheep with two horns: and the two horns were high, but one was higher than the other, the higher one coming up last.
Daniel 11:1-2
1 And as for me, in the first year of Darius the Mede I was on his side to make his position safe and make him strong.
2 And now I will make clear to you what is true. There are still three kings to come in Persia, and the fourth will have much greater wealth than all of them: and when he has become strong through his wealth, he will put his forces in motion against all the kingdoms of Greece.