When were the Jewish temples destroyed?
The Jewish fast day of Tisha B’Av, the ninth day of the Hebrew month Av, occurring in 2014 on the eve of August 4 and the day of August 5, commemorates the destruction of the first and second Temples. However, neither temple was razed on the ninth of Av. The first temple was demolished by the Babylonians on the seventh of Av according to II Kings 25:8–9 and the tenth of Av according to Jeremiah 3:12, in 586 BCE. Tosefta Ta’anit 4:10 and the Babylonian Talmud, Ta’anit 29a, explain the discrepancy between the seventh and the tenth: the outer walls were demolished on the seventh and the temple itself on the tenth.
The second temple was destroyed by the Romans on the tenth of Av in 70 CE, according to the historian and Jewish general Josephus in his Wars 6:249-250. Josephus was present at the occurrence. But the Babylonian Talmud, Ta’anit 29a, several centuries later, gives the date as the ninth of Av.
Why did the rabbis say the demolition of the first and second temples occurred on the ninth of Av when evidence exists that these events did not occur on the ninth? We do not know. But it is possible that the rabbis didn’t want to associate the destruction of the temples with the numbers seven, eight, and ten.
It could be that the rabbis rejected seven because seven is used frequently in the Bible to denote completeness, and it reminds us of the Sabbath and joy, and the rabbis did not want to give the impression that Judaism was completely destroyed and that there is joy connected to the event.
Eight may not have been chosen since eight was seen as a symbol of a new beginning since it follows seven, and the temple destruction was not a new beginning, but the end of an era. Similarly, ten may have seemed inappropriate because ten is made up of seven and three, the two numbers used in the Bible for completeness.
It is also possible that the rabbis did not choose to have the fast of Av on the tenth because the tenth would remind Jews of the other fast of the tenth, Yom Kippur, and they didn’t like having Jews to compare both days. The fast of Av is considered an enormous and total calamity. Yom Kippur, on the other hand, has positive elements: during the temple days, the afternoon of Yom Hakippurim, as it was called in the Torah, was a happy time when young boys and girls would meet and dance. Additionally, on Yom Kippur one is able to seek forgiveness and repair past misdeeds.
 Tisha is Hebrew for nine.
 Since the Jewish day begins in the evening.
 Abraham ibn Ezra explains that seven indicates something is complete while three, being close to half seven, suggest a smaller completeness, such as Abraham taking a trip for three days.
 As I explain in my recent book “Mysteries of Judaism.”