As Jesus left and was going out of the temple, his disciples came up and called his attention to its buildings. He replied to them, “Do you see all these things? Truly I tell you, not one stone will be left here on another that will not be thrown down.”
Matthew 24:1-2 | cross ref: Mark 13:1-2 and Luke 21:5-6.

This prophecy of judgment was fulfilled when Rome destroyed Jerusalem in AD 70. Between AD 66 and AD 135, the Jews led a series of large-scale revolts against the Roman Empire. Three large conflicts (First Jewish–Roman War, Diaspora Revolt, and Bar Kokhba Revolt), resulted in catastrophic consequences for the Jewish population in Judaea, resulting in massive loss of life, widespread enslavement, and extensive forced displacement. In response to the Jewish revolt in AD 70, the Roman Empire laid siege to Jerusalem for five months. Next, the city was invaded and ransacked, bringing the Jewish death toll into the hundreds of thousands. Romans burned the temple, causing leftover gold to melt into the cracks of the masonry. To remove it, soldiers literally tore the structure apart brick-by-brick, leaving nothing left but the level foundation. At that point, Jesus’s prophecy was completely fulfilled. The Jewish-Roman wars profoundly transformed the Jewish people, converting a once-prominent population in the Eastern Mediterranean into a dispersed and persecuted minority. These conflicts caused extensive casualties and destruction throughout Judea and led to mass displacement and the enslavement of many. While the First Jewish-Roman War devastated Jerusalem – destroying the center of Jewish political, national, and religious life – the Bar Kokhba revolt had even more catastrophic consequences, effectively depopulating Judea, the core of the Jewish homeland, of its Jewish population. The defeat also ended aspirations for Jewish political independence in the region for nearly two millennia.
See What does Matthew 24:2 mean? via BibleRef and Jewish-Roman Wars via Wikipedia.