Shiva Asar BeTammuz - The Fast of 17th Tammuz This fast commemorates a number of events: The breaching of the walls of Jerusalem by the Romans The day that Moses broke the two tablets of the Law (according to tradition) Apostomos, a Greek, burnt the Torah The regular daily sacrifice ceased in the Temple The 17thTammuz ushers in the Three Weeks of national mourning till the 9th Av, during which the pious abstain from every kind of celebration.