Daniel 2:33
its legs of iron, its feet partly of iron and partly of clay [pottery].
Daniel 2:40-43
Then a fourth kingdom (Rome) will be strong as iron, for iron breaks to pieces and shatters all things; and like iron which crushes things in pieces, it will break and crush all these [others].
Daniel 7:7-8
After this I kept looking in the night visions, and behold, [I saw] a fourth beast (the Roman Empire), terrible and extremely strong; and it had huge iron teeth. It devoured and crushed and trampled down what was left with its feet. It was different from all the beasts that came before it, and it had ten horns (ten kings).
Daniel 7:19-26
“Then I wished to know the exact meaning of the fourth beast, which was different from all the others, extremely dreadful, with teeth of iron and claws of bronze, which devoured, crushed and trampled down what was left with its feet,