'Iron' in the Bible

And the Lord was with Judah; and he took the hill-country for his heritage; but he was unable to make the people of the valley go out, for they had war-carriages of iron.

Then the children of Israel made prayer to the Lord; for he had nine hundred iron war-carriages, and for twenty years he was very cruel to the children of Israel.

So Sisera got together all his war-carriages, nine hundred war-carriages of iron, and all the people who were with him, from Harosheth of the Gentiles as far as the river Kishon.