Which event caused yohanan ben zakkai to start a school for rabbis?

Yohanan Ben Zakkai was able to put up a school for rabbis due to the permission of Vespasian, a Roman general. When the city where Zakkai lived was under siege by Vespasian, he faked his death so that he can hide inside a coffin and his pupils can bring him out of the city. He told Vespasian that he had a vision of the general would soon be an emperor, and he requested that his city be spared from war and for him to be able to build a school. Vespasian agreed that if the prophesy came true, he will grant his request. After becoming the emperor, Ben Zakkai was able to put up his school. 

James wattrichard arkwright eli whitney thomas edisonnicolaus otto