We begin now our study of the four fast days which were decreed by the Prophets in commemoration of national calamities which occurred on those days. Let us review from our previous lesson the purpose of a fast day. We quote from A Summary of the Halachos of the Three Weeks, by Rav Shimon Eider zt”l, p. 1:
“The purpose of a fast day is to stir our hearts in order that we utilize the paths of Teshuva, repentance, and to serve as a reminder to us of our own actions and those of our forefathers. These iniquities are responsible for the terrible events which befell our people. Remembering these tragedies should lead us to examine our conduct and return to Hashem. One should not mistakenly assume that abstinence from food and drink alone fulfils the requirement and purpose of a fast day. When the sinful city of Ninveh repented, the pasuk (Yonah 3:10) says, “Hashem saw their actions.” Chazal emphasize that fasting and wearing sackcloth alone would have been meaningless, were it not for the altering of their evil ways. Thus the true purpose of a fast day must be evidenced in one’s improved deeds.”
We have a pasuk in Sefer Zecharia (8:19) which states: “Thus says Hashem, Master of Legions: The fast of the fourth month (Ed. Starting from Nisan, that is Tamuz), the fast of the fifth (Av), the fast of the seventh (Tishrei) and the fast of the tenth (Teves) will be to the House of Judah for joy and for gladness and for happy festivals. Only love truth and peace!” The Navi (prophet) Zecharia prophesied during the period between the destruction of the first Beis Hamikdash and the building of the second, and it is over the tragic events of the desecration and destruction of the First Temple that the four fasts listed in the pasuk were ordained. The Navi is comforting the Jewish people that one day these days will no longer be days of mourning and fasting but of rejoicing and rebuilding! According to the Gemara Rosh Hashana 18b, these fast days were mandatory only during the Babylonian exile, following the destruction of the First Temple. Once the Second Temple was rebuilt, and the immediate decrees against the Jews were suspended, the four fast days were not mandatory; rather it was left to the discretion of each community and its Beis Din, whether or not its residents would observe them as fast days. Our sources teach that later in history, as new decrees and persecutions arose, it was universally accepted and legislated that these fast days would be reinstated as mandatory until the time of the Final Redemption. In fact, by the time of the redaction of the Talmud (several hundred years after the destruction of the Second Temple), these same dates were revisited by tragedies of the Second Temple era as well.
What follows is a chart of the names of the four fasts, their respective dates, what tragedy/-ies transpired on each, and during what time-period(s) it occurred. (Ed: The order of the chart follows the order of the Shulchan Aruch, not the order of the pasuk in Zecharya.)