The city is massively fortified. It also has huge storehouses of food. It has a good water supply. Jerusalem can hold back the Romans for a long time. So it seems like the Romans are in a very bad situation. They are trying to besiege one of the largest cities in the ancient world which is remarkably well fortified, which has a huge amount of food and water and a lot of determined people who are not afraid to die. Jerusalem could have gone done down in history as the only city that the Romans couldn't take by laying siege. But it didn't. The reason that it did not was sinat chinam, "senseless hatred among the Jews."
CIVIL WAR While the Romans are besieging the city on the outside, the Jews are waging a civil war inside. Forces of the various factions are occupying various parts of the city. Most importantly, the Sicarii and the Zealots, led by Yochanan of Gush Chalav, have control of the Temple Mount. The unholy alliance of Sadducees and Pharisees makes up the bulk of the moderate forces which rule the rest of the city. When the moderates attempt to remove the extremists from the Temple Mount, The Zealots bring Yochanan of Gush Chalav brings in non-Jewish mercenaries, the Idumeans, who in non-Jewish slaughter the moderate Jews.
mercenaries, who slaughter the As if that is not enough, the Zealots destroy the great storehouses of food so that the moderate Jews. people would have no choice but to fight or starve. With the food storehouses destroyed, famine breaks out in the city and desparate people try and sneak outside the walls to forage for food. Anyone that is caught by the Romans is immediately put to death via the standard Roman form of execution - crucifixion. So many die that the city is surrounded by thousands of crucified Jews. Meanwhile, the Romans continue their systematic destructions of the city's defenses, layer by layer. What happens next?
YOCHANAN BEN ZAKKAI The leader of the Pharisees, Rabbi Yochanan ben Zakkai, sees that Jerusalem cannot hold out. It's too late. But the Zealots are bent on continuing their suicidal fight. So he formulates a plan. At this time the Zealots are not allowing anyone to leave the city (as if anyone wanted to flee to be crucified), except for burials. In a desperate bid to try and salvage something from the impending disaster, Rabbi Yochanan ben Zakkai has himself put in a casket and taken to Vespasian. He greets Vespasian as if he were the emperor, to which Vespasian replies that he ought to be executed for his remark. Not exactly a friendly welcome. But Rabbi Yochanan ben Zakkai persists, telling Vespasian that God would allow only a great ruler to take Jerusalem.