The Siege of Jerusalem in 70 CE is arguably the most important event in Jewish history. First, it was the central battle in the First Jewish-Roman war. Second, the failure of the siege on the Jewish side resulted in the destruction of the Second Temple of Jerusalem, a disaster that would eventually prove both permanent and catastrophic, since it was never rebuilt. Third, it permanently altered the diaspora of Judaism in the ancient world. Fourth, because it was indecisive in breaking the power of the Jewish revolt permanently, it was also inconclusive and led to further, inevitable revolts that broke Judean identity completely.

It was not the first time the Romans had conquered the capital of the kingdom, nor was it the first time Jerusalem had been sacked by a foreign power. It was unusual for the Romans, however, because it was not the final act that such a conquest generally was. With few exceptions, such as the Carthaginians and the Celts, the Romans had not encountered an opponent who refused to remain defeated. Roman generals and governors found this stubborn resistance unnerving and that may have contributed to an increased cruelty toward the local Jewish population, not that the Romans generally required an excuse to be brutal.

To the Romans' bewilderment, the Jews were absolutely, adamantly opposed to worshiping any deity above God (in the universal form of Yahweh), or even alongside or beneath God. At this point in their theological history, the Jews had become strict monotheists. Worshiping the Emperor as a deity would imperil their immortal souls. Therefore, they absolutely refused to do this and were willing to die for their faith. The Jewish refusal to tolerate the cult of the emperor in their main place of worship was a direct challenge to Roman political power. The Roman refusal to recognize Jewish monotheism was a direct challenge to Jewish theology. The clash of ideologies would result in many casualties. Josephus, a primary source for the revolt, would calculate the death toll at over 1,000,000.

The Siege of Masada was the final battle in a long series of fights that constituted the First Jewish-Roman War. However, what made this battle qualitatively different from most was not just the difficulty Rome had in retaking control of it with incredibly disproportional military equipment and numbers, but also the actions of the Judean defenders. In the final hours of the battle, just as the Romans were about to breach the walls of the city, the defenders gathered together and committed mass suicide, rather than being killed or taken captive by the Romans.