Daniel 2:31

Terrible, or unusual. (Calmet) --- The statue denoted the four great empires of the Chaldees, Persians, Greeks and Romans. The metals did not mean that the empire of gold was greater than the rest, as that signified by iron was far more powerful; but only that the empire of the Chaldees was then the greatest, and that the Persians would acquire still more power and be surpassed by the Greeks, as they were by the Romans, till the kingdom of Christ should be spread over all the earth. (Worthington)