Daniel 2:40 (BSB)

Finally, there will be a fourth kingdom as strong as iron; for iron shatters and crushes all things, and like iron that crushes all things, it will shatter and crush all the others.

From Daniel 2. Also in the ESV.

Commentary on Daniel 2:40

• John Calvin (Reformed), Calvin's Commentaries on Daniel 2:40: Here the Fourth Empire is described, which agrees only with the Roman, for we know that the four successors of Alexander were at length subdued. Philip was the first king of Macedon, and Antiochus the second; but yet Philip lost nothing from his own kingdom; he only yielded it to the free cities of Greece.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Daniel 2:31-45: Daniel here gives full satisfaction to Nebuchadnezzar concerning his dream and the interpretation of it. That great prince had been kind to this poor prophet in his maintenance and education; he had been brought up at the king's cost, preferred at court, and the land of his captivity had hereby been made much easier to him than to others of his brethren.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Daniel 2:40: And the fourth kingdom shall be strong as iron,.... This is not the kingdom of the Lagidae and Seleucidae, the successors of Alexander, as some have thought; for these are designed by the thighs in the third kingdom; and, besides, the kingdom of Christ was to arise in the time of this fourth kingdom, which it did not in that; nor the kingdom of Gog...
• Jamieson-Fausset-Brown (Reformed), Commentary Critical and Explanatory on the Whole Bible on Daniel 2:40: iron--This vision sets forth the character of the Roman power, rather than its territorial extent [TREGELLES]. breaketh in pieces--So, in righteous retribution, itself will at last be broken in pieces (Dan 2:44) by the kingdom of God (Rev 13:10).