Daniel 8:3-4
History records that the Persians considered a ram with sharp, pointed horns to be their guardian spirit, and the king bore the head of a ram instead of a crown when he led his armies into battle. The symbols of Medo-Persia used in the Bible, the ram and the bear, are powerful creatures, as opposed to the quick and agile goat and leopard, representing Greece. As for the different heights of the horns, the taller one represents the Persian half of the empire that rose to power later than the Median half.
Both the Medes and the Persians, as the Bible shows are represented by these horns (Daniel 8:20), also had territories located near the Tigris and Euphrates rivers. Though it makes little difference in the prophecy's interpretation, this river could also be "the River Ulai" (Daniel 8:2) upon whose banks the Persian capital of Susa (Shushan) was built.
The ram's pushing in every direction except east reflects the historical reality that Persia's eastern campaigns were inconsequential as compared to its other conquests. Though they did conquer as far east as the Indus River, subjugating Asia Minor, Babylon, Egypt, and Armenia was much more significant. Persia felt very little resistance in the east, and in its later history the western Macedonians under Alexander, represented by the he-goat with a notable horn (verse 21), were its most challenging foes.
Richard T. Ritenbaugh
Nebuchadnezzar's Image (Part Two): Chest and Arms of Silver