הָאַ֥יִל אֲשֶׁר־רָאִ֖יתָ בַּ֣עַל הַקְּרָנָ֑יִם מַלְכֵ֖י מָדַ֥י וּפָרָֽס׃
The ram which thou sawest having the two horns, they are the kings of Media and Persia.
Rashi on Daniel
The kings of Media and Persia The two horns represent two ruling nations, as I explained above.