The Ninth of Av (Tisha B’Av) is the most serious fast day on the Jewish calendar besides Yom Kippur and lasts from sunset to sunset. It is one of four similar biblical fast days mentioned by the Prophets. It may be moved if its observance would conflict with Shabbat.
The fast of the fifth month (Zec. 7:3f, 8:19). The generation in the wilderness is condemned to wander for 40 years and die in the wilderness (tradition, Num. 14). “‘As I live,’ says the LORD, ‘just as you have spoken in My hearing, so I will surely do to you; your corpses will fall in this wilderness, even all your numbered men, according to your complete number from twenty years old and upward.”
The First Temple is destroyed by the Babylonians year 586 BCE (tradition, 2 Ki. 25:9). The second Temple is destroyed by the Romans year 70 CE (tradition). “As he approached Jerusalem and saw the city, he wept over it and said, “... They will dash you to the ground, you and the children within your walls. They will not leave one stone on another” (Lk. 19:41,44 NIV). The Bar Kochba revolt is crushed by the Romans at Beitar (133 CE).
The Jews are expelled from England by King Edward I (1290 CE). The Jews are expelled from Spain by King Ferdinand och Queen Isabella (1492 CE). The Nazis begin the mass deportation of Jews from the Warsaw Ghetto, en route to Treblinka death camp (1942 CE)