The Seventeenth day of the month of Tammuz is a Jewish day of mourning and fasting. It is the first day of the Three Weeks, which climax in Tisha ba Av.
It seems that a fast in Tammuz is ancient in origin. Zechariah refers to "The fast of the fourth month" (Zech 8:19), but it's not clear that it's on the seventeenth; a more likely candidate is the 9th of Tammuz, the date that Nebuchadnezzar's army breached the wall of Jerusalem in the time of the First Temple.
The Seventeenth of Tammuz was the date when, in the year 70CE, Titus's troops breached the wall of Jerusalem after a long siege. This marked the beginning of the destruction of Jerusalem and the Second Temple.
The Seventeenth of Tammuz absorbed the earlier fast day, because their purposes and dates were so similar.
According to the Mishna (Taanit 4:6) a variety of other tragedies also occurred on this date:
In more modern times, the date has been unlucky for the Jewish people. Modern disasters on the Seventeenth of Tammuz include:
- In 1239 Pope Gregory IX ordered the confiscation of all copies of the Talmud
- 4000 Jews were killed in Toledo in Spain, in 1391
- In 1559 the Jewish Quarter of Prague was attacked and looted.
- In 1944, the Kovno Ghetto was liquidated and its inhabitants sent to death camps.
- In 1970, all Jewish property in Libya was confiscated by the government
The Seventeenth of Tammuz is considered a minor fast day. This means that eating and drinking of any kind are forbidden from sunrise until sunset. People who are unwell, children and pregnant women don't have to fast, though they shouldn't eat extravagantly.
As the Seventeenth of Tammuz is also the beginning of the Three Weeks, the prohibitions that apply for the whole Three Weeks also come into effect. This means listening to music, buying new clothes, and (for Ashkenazim) shaving or having a haircut are also forbidden.
Minor fast days aren't observed on a Saturday or Friday, out of respect for Shabbat. If the 17th of Tammuz falls on a Saturday or Friday, the fast is held on the Sunday instead.