Tisha B'Av occurs on the 9th day of the Hebrew month of Av. It commemorates a number of disastors in Jewish History, primarily the destruction of both Solomon's Temple by the Neo Babylonian Empire and the Second Temple by the Roman Empire in Jerusalem. It precedes the end of the three weeks between dire straits. This day is regarded as the saddest day in the Jewish calendar and may Jews fast for 25 hours.