The ninth of the Hebrew month of Av is a major fast day in the Jewish calendar, when the people lament the date of the destruction of both, the First and the Second Temples, with the subsequent loss of national sovereignty and exile from the Holy Land.
Tischa B’Av is the culmination of three week period of mourning, the last nine days of which are particularly intense, with observance of many customs similar to those practised after a bereavement in the close family. The »Three Weeks«, as they are known,

Westwall Jerusalem

begin on the seventeenth of the month of Tammuz, the date on which the outer walls of the City of Jerusalem were breached during the siege. This is also the date on which Moses broke the first tablets of the law when he came down from Mt. Sinai after 40 days - to find the people worshipping the Golden Calf.
The Ninth of Av is the date on which the Betar stronghold fell, the date of the Jewish expulsion from Spain in 1492, the beginning of Nazi deportations of Jews from the Warsaw Ghetto...
The day is marked publicly in the State of Israel by the closure of restaurants, places of entertainment etc. from the previous evening, with food shops opening only for morning hours. The day is interpreted through its religious significance and / or its importance in connection with nationhood and national sovereignty - whether or not individuals choose to fast. Traditional observance includes the reading of the Book of Lamentations, the Kinot, a 25 hour fast, deprivation of comfort and physical contact. In Jerusalem, thousands of people stream towards the Kotel, the Western and only remaining Wall of the Second Temple to commemorate the destruction and pray of redemption.

»When the month of Av begins, we reduce our joy...«
(Talmud, Ta’anit 26)