Daniel 7:19
Then I had the desire to know the truth regarding the fourth beast, which was so different from all the others, exceeding dreadful, whose teeth were of iron, and its nails of brass; which devoured and broke in pieces and trod down that which was left with its feet;
Daniel 7:7
After this I saw in the night visions, and behold the fourth beast, dreadful and terrible, and exceedingly strong; and it had great iron teeth; it devoured and broke in pieces and trod down that which was left with its feet; and it was very different from all the beasts that had been before her; and it had ten horns.
Daniel 2:40-43
And the fourth kingdom shall be strong as iron; and as iron breaks in pieces and subdues all things, and as iron that breaks all these things, it shall break in pieces and bruise.