Because it's in Daniel.

The Roman empire was the Iron mixed with clay, and the stone that broke it was Jesus who set up is final kingdom, that was left to the Germanic tribes who make up all of Europe at present day. (tldr)


Daniel 2
>34 As you were watching, a stone broke off without a hand touching it,[h] struck the statue on its feet of iron and fired clay, and crushed them. 35 Then the iron, the fired clay, the bronze, the silver, and the gold were shattered and became like chaff from the summer threshing floors. The wind carried them away, and not a trace of them could be found. But the stone that struck the statue became a great mountain and filled the whole earth.

>43 You saw the iron mixed with clay—the peoples will mix with one another[j] but will not hold together, just as iron does not mix with fired clay.

>44 “In the days of those kings, the God of heaven will set up a kingdom that will never be destroyed, and this kingdom will not be left to another people. It will crush all these kingdoms and bring them to an end, but will itself endure forever. 45 You saw a stone break off from the mountain without a hand touching it,[k] and it crushed the iron, bronze, fired clay, silver, and gold. The great God has told the king what will happen in the future.[l] The dream is true, and its interpretation certain.”