Tuesday marks the 17th of Tammuz on the Jewish calendar, a pre-dawn-to-evening fast, which marks a number of tragedies in Jewish history and opens a three-week mourning period leading up to the anniversary of the destruction of the first two holy Temples in Jerusalem on the 9th of Av. The fast will end at 8:16 in Jerusalem.
The tragedy associated with the destruction of the Temples is the breaching of the walls of Jerusalem by the Romans before the destruction of the Second Temple. The daily sacrifices stopped, and idol was placed in the Temple and Roman military leader Apostomus burned a Toral scroll before the Bar Cochva rebellion. The first tragedy was the breaking of the first stone tablets of the Ten Commandments following the Sin of the Golden Calf.