Daniel 7:19
Then I desired to know the truth concerning the fourth animal, which was diverse from all of them, exceedingly terrible, whose teeth were of iron, and its nails of brass; which devoured, broke in pieces, and stamped the residue with its feet;
Daniel 7:7
After this I saw in the night visions, and, behold, a fourth animal, awesome and powerful, and strong exceedingly; and it had great iron teeth; it devoured and broke in pieces, and stamped the residue with its feet: and it was diverse from all the animals that were before it; and it had ten horns.
Daniel 2:40-43
The fourth kingdom shall be strong as iron, because iron breaks in pieces and subdues all things; and as iron that crushes all these, shall it break in pieces and crush.