Here's some background on the 17th of Tammuz:
The 17th of Tammuz is a fast day commemorating the fall of Jerusalem, prior to the destruction of the Holy Temple. This also marks the beginning of a 3-week national period of mourning, leading up to Tisha B'Av.Here's an overview of the laws relating to the period of the Three Weeks.
The 17th of Tammuz is the first of four fast days mentioned in the prophets. The purpose of a fast day is to awaken our sense of loss over the destroyed Temple - and the subsequent Jewish journey into exile.[...]
Five great catastrophes occurred in Jewish history on the 17th of Tammuz:
*Moses broke the tablets at Mount Sinai — in response to the sin of the Golden Calf.
*The daily offerings in the First Temple were suspended during the siege of Jerusalem, after the Kohanim could no longer obtain animals.
*Jerusalem's walls were breached, prior to the destruction of the Second Temple in 70 CE.
*Prior to the Great Revolt, the Roman general Apostamos burned a Torah scroll - setting a precedent for the horrifying burning of Jewish books throughout the centuries.
*An idolatrous image was placed in the Sanctuary of the Holy Temple - a brazen act of blasphemy and desecration.
(Originally, the fast was observed on the Ninth of Tammuz since that was the day Jerusalem fell prior to the destruction of the First Temple in 586 BCE. However, after Jerusalem fell on the 17th of Tammuz - prior to the destruction of the Second Temple - the Sages decided upon a combined observance for both tragedies, the 17th of Tammuz.)
The "Three Weeks" between the 17th of Tammuz and the Tisha B'Av have historically been days of misfortune and calamity for the Jewish people. During this time, both the First and Second Temples were destroyed, amongst other terrible tragedies.The Nine Days, starting on the 1st day of Av start an strict period of morning.
These days are referred to as the period "within the straits" (bein hametzarim), in accordance with the verse: "all her oppressors have overtaken her within the straits" (Lamentations 1:3).
On Shabbat during the Three Weeks, the Haftorahs are taken from chapters in Isaiah and Jeremiah dealing with the Temple's destruction and the exile of the Jewish people.
During this time, various aspects of mourning are observed by the entire nation. We minimize joy and celebration. And, since the attribute of Divine judgement (“din”) is acutely felt, we avoid potentially dangerous or risky endeavors.
ASPECTS OF MOURNING DURING THE THREE WEEKS
1. No weddings are held. (However, engagement ceremonies are permitted.)
2. We do not listen to music.
3. We avoid all public celebrations -- especially those which involve singing, dancing and musical accompaniment.
4. We avoid pleasure trips or other unusually entertaining activities.
5. No haircuts or shaving. (Fingernails may be clipped up until the week in which Tisha B'Av falls.)
6. We do not say the blessing She-hechianu on new food or clothes, except on Shabbat.
1. We avoid purchasing any items that bring great joy.What happened on Tisha B'Av?
2. We suspend home improvements, or the planting of trees and flowers.
3. We avoid litigation with non-Jews, since fortune is inauspicious at this time.
4. We abstain from the consumption of meat (including poultry) and wine. These foods are symbolic of the Temple service, and are generally expressions of celebration and joy.
**On Shabbat, meat and wine are permitted. This applies also to any other seuduat mitzvah -- for example, at a Brit Milah or at the completion of a tractate of Talmud.
**Wine from Havdallah should be given to a child to drink.
5. We refrain from wearing newly laundered garments, or laundering any clothes.
**If the "freshness" has been taken out of a garment prior to the Nine Days, it may be worn.
**Fresh clothes may be worn for Shabbat.
**The clothing of small children, which gets soiled frequently, may be laundered during the Nine Days.
**Clothes may not be laundered even if done in preparation for after Tisha B'Av, or even if done by a non-Jew.
6. We do not bathe for pleasure.
**It is permitted to bathe in order to remove dirt or perspiration, or for medical reasons. This may be done only in cool water.
**Furthermore, the body should be washed in parts, rather than all at one time.
**Bathing in warm water is permitted on Friday in honor of Shabbat.
On Tisha B'Av, five national calamities occurred:Some other misfortunates that came our way:
1. During the time of Moses, Jews in the desert accepted the slanderous report of the 10 Spies, and the decree was issued forbidding them from entering the Land of Israel. (1312 BCE)
2. The First Temple was destroyed by the Babylonians, led by Nebuchadnezzar. 100,000 Jews were slaughtered and millions more exiled. (586 BCE)
3. The Second Temple was destroyed by the Romans, led by Titus. Some two million Jews died, and another one million were exiled. (70 CE)
4. The Bar Kochba revolt was crushed by Roman Emperor Hadrian. The city of Betar -- the Jews' last stand against the Romans -- was captured and liquidated. Over 100,000 Jews were slaughtered. (135 CE)
5. The Temple area and its surroundings were plowed under by the Roman general Turnus Rufus. Jerusalem was rebuilt as a pagan city -- renamed Aelia Capitolina -- and access was forbidden to Jews.
1. The Spanish Inquisition culminated with the expulsion of Jews from Spain on Tisha B'Av in 1492.
2. World War One broke out on the eve of Tisha B'Av in 1914 when Germany declared war on Russia. German resentment from the war set the stage for the Holocaust.
3. On the eve of Tisha B'Av 1942, the mass deportation began of Jews from the Warsaw Ghetto, en route to Treblinka.