Daniel 2:31 - Coke's Commentary on the Holy Bible

Behold a great image— It appears from ancient coins and medals, that cities and people were often represented by the figures of men and women. A great and terrible human figure was therefore no improper emblem of human power and dominion; and the various metals of which it was composed, not unfitly typify the various kingdoms which should arise. It consisted of four different metals, gold, silver, and brass, mixed with iron and clay; and these four metals, according to Daniel's own interpretation, mean so many kingdoms; and the order of the succession is clearly denoted by the order of the parts; the head and higher parts signify the earlier times, and the lower parts the later times. Hesiod, who lived two hundred years before Daniel, mentioned the four ages of the world under the symbols of these metals; so that this vision, according to the good pleasure of God, was formed according to the commonly received notion, and the commonly received notion was not first propagated from this vision. See Bishop Newton, and Chandler's Defence, p. 96.