Today, the 17th day of Tammuz, is a day of fasting that marks the beginning of a three-week period of national mourning. The Jewish Sages set aside this date to commemorate the beginning of the fall of Jerusalem and the destruction of both the First and Second Temples, some 2,500 and 2,000 years ago, respectively.
The three-week period of mourning culminates on Tisha B'Av, the ninth day of the month of Av, on which the Temples were actually destroyed.
The Prophet Zechariah (8,19) foretold that the days of fasting over Jerusalem will one day "become for the House of Judah gladness and joy and happy holidays."
The 17th of Tammuz also marks the day on which: Moses broke the original Tablets of the Law in response to the Sin of the Golden Calf; the daily sacrifice could no longer be offered in the First Temple; the walls of Jerusalem were broken through during the Second Temple period; the Roman conqueror Apostemus burned a Torah Scroll in the Temple; and an idol was placed inside the Temple.
The three-week period of mourning culminates on Tisha B'Av, the ninth day of the month of Av, on which the Temples were actually destroyed.
The Prophet Zechariah (8,19) foretold that the days of fasting over Jerusalem will one day "become for the House of Judah gladness and joy and happy holidays."
The 17th of Tammuz also marks the day on which: Moses broke the original Tablets of the Law in response to the Sin of the Golden Calf; the daily sacrifice could no longer be offered in the First Temple; the walls of Jerusalem were broken through during the Second Temple period; the Roman conqueror Apostemus burned a Torah Scroll in the Temple; and an idol was placed inside the Temple.