Fasts observed for events that did not occur on the day of the fast
There are two extended mourning periods in the Jewish calendar, one for three weeks and the other for seven. Both are not based on verifiable facts and dates, both are not biblical since the events occurred after the days of Moses, but each reminds Jews of their history and encourages Jews to think about and help the State of Israel. Both mourning periods occur during the summer.
The three weeks
The three weeks begins on the seventeenth of the Hebrew month Tammuz, and is called a minor fast day, meaning the fast begins in the morning rather than sundown of the prior day, when the day begins according to Jewish tradition. Yom Kippur and 9 Av are major fasts because the fasts begin at sunset when the day starts. In 2015, 17 Tammuz, the fast that starts the three weeks, occurs on Saturday, July 4 and 9 Av, which ends it, is on Sunday, July 26.
The fast of 17 Tammuz is first mentioned in the biblical book Zechariah 8:19. It commemorates the beginning of the siege of Jerusalem’s walls during the second Temple period, in 70 CE. However, while Zechariah cites the month of the fast day, it does not give the date. The Babylonian Talmud, Taanit 26a and b, states that four additional tragedies happened on 17 Tammuz: Moses broke the first set of the Decalogue, The Romans placed an idol in the Temple’s inner sanctum during the second Temple period before they destroyed the Temple, the twice daily sacrifices offered in the Temple was forcibly discontinued, and a Roman military leader burned a Torah scroll. There is no historical evidence that any of these four events or the fifth, the onset of the siege, occurred on 17 Tammuz, other than Jewish tradition.
Practices during the three weeks
Traditions differ what Jews do during the three weeks, until 9 Ab. Some Jews, like people in other cultures and religions, do not observe all the culture’s and religion’s practices, and don’t fast on either of these two fast days and behave as usual during the three weeks. Some fast only on 9 Ab and ignore 17 Tammuz. Some fast on both days but vary how they treat the middle period. Some mourn the loss of the two Temples by refraining from pleasures either during the entire three weeks, the nine days of Ab, or for the last three days before 9 Ab. Many recall the ancient tragedies and mourn them by not eating meat dishes during the nine days of Ab, because they consider meat better foods and improper consumptions during mourning periods, and by not having a haircut, or men shaving. The Talmud of the sixth century does not mention the three week period, but it discusses the different behaviors of people during the nine days of Ab.
The date of 9 Ab, which current tradition states commemorates the destruction of both the first and second Temples in Jerusalem, in 586 BCE and 70 CE, respectively, like the seventeenth of Tammuz, is not based on historical facts. We no longer know why the seventeenth or ninth was chosen for the fasts. Interestingly, we have dates when the Temples were destroyed and they are not 9 Ab. The biblical book II Kings 15:8 states that the first Temple was destroyed on 7 Ab, while the biblical book Jeremiah gives the tenth as the destruction date. Tosefta Taanit 4:6 and Babylonian Talmud, Taanit 29a, try to resolve the apparent discrepancies by stating that the destruction of the first Temple by the Babylonians began on the seventh, they ignited a fire in the Temple on the ninth, and it continued to burn on the tenth. The historian Josephus, who lived when the second Temple was destroyed and saw it burn, gives the destruction date as 10 Ab in his book Wars of the Jews 249-250.
The Babylonian Talmud, Taanit 26b, states that three additional events occurred on the ninth of Ab, beside the two destructions: this was the day when the decree was issued that the Israelites could not enter Canaan but must remain in the desert for forty years, the city of Bethar was destroyed during the Bar Kochba rebellion of 132-135 CE, and the Romans ploughed up Jerusalem. There is no evidence, historical or otherwise, that these events occurred on 9 Ab. Significantly, the Talmud is telling us that both fast days recall five tragic events.
The Second Temple was destroyed in the same month as the First Temple. This made a tremendous impression upon the Jews. In the words of Josephus, “One cannot but wonder of the accuracy of this period thereto relating; for the same month and day were now observed wherein the holy house was burnt formerly by the Babylonians (Wars of the Jews 6:268).” Some sages understood this to be far more than coincidence. They believed that God ordains events so that positive developments occur on auspicious days and tragedies occur on days predestined for disaster (Babylonian Talmud, Ta’anit 29a). They go so far as to advise people not to undertake any new venture on 9 Av because the day is so unlucky it is sure the venture will fail.
Observance of the fast on the Sabbath
Judaism feels that the Sabbath is such a festive day that Jews should not fast on the Sabbath. Some fasts are therefore pushed ahead and observed on the preceding Thursday or Friday. Others are postponed until Sunday. The Mishnah lists several ceremonies that are postponed, including 9 Ab (Mishnah Megillah 1:3). Although not mentioned in this Mishnah, the fast of 17 Tammuz is also postponed this year to Sunday. The fast of 17 Tammuz reoccurs on a Saturday on July 23, 2016.
What does this tell us?
Since none of these fast days commemorate events that occurred on the precise date of the event, we see that Jewish ancestors instituted these fasts around the time of the event, even though it is not the exact date in which the events occurred. This is similar to the holiday of Shavuot, Pentecost. During the Middle Ages, Shavuot was given the meaning that it remembers the time when the Decalogue (Ten Commandments) were given to the Israelites. Shavuot is called in Hebrew zeman matan torateinu, “the season of the giving of the Torah,” but not the precise date, because the Torah does not give the exact date for the revelation of the Decalogue.