And he came to the ram that had two horns, which I had seen standing before the river, and ran at him in the fury of his power.
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Aquinas Study Bible
The ram was the King of Media and Persia, that is, Darius; and the he-goat was Alexander, the son of Philip, the Macedonian. (Aphrahat) The two horns are the two powers, which Darius possessed, as the kingdom was subjected to two races, since the Medes and Persians were indicated together. (Ishodad of Merv) notable horn: refers to the first king, Alexander himself. (St. Jerome)