.. Tisha B'Av ..     Tisha B'Av is regarded as the saddest day in the Jewish calendar  and a day which is destined for tragedy.     The observance is held on the 9th day in the month of Av.     ..     It is an annual 25-hour fast day in Judaism   which commemorates the anniversary of a number of disasters in Jewish history,   primarily the destruction of both the First and Second Temples in Jerusalem.     ..     The day has become associated with remembrance of other major disasters  which have befallen the Jewish people,   such as the murder of the Ten Martyrs   and massacres in numerous medieval Jewish communities  during the Crusades  and the Holocaust.     ..