The Babylonian Jews wanted to fight in common cause with their Judean brethren against Vespasian; but it was not until the Romans waged war under Trajan against Parthia that they made their hatred felt; so, the revolt of the Babylonian Jews helped prevent Rome from becoming master there. Philo speaks of the numerous Jews resident in that country, a population that was likely increased by immigrants after the destruction of Jerusalem. In Jerusalem from early times, Jews had looked to the east for help. With the fall of Jerusalem, Babylonia became a kind of bulwark of Judaism. The collapse of the Bar Kochba revolt likely also added to Jewish refugees in Babylon.