On the Hebrew calendar, the 9th day of Av (Tisha b’Av in Hebrew) is a notorious date of tragedy for the Jewish people. Many major tragedies are recorded in the Bible and continue up to modern history.
The Bible tells us that Aaron died on the first day of Av. Although he was a faithful servant for 40 years, he was part of that first generation that did not get to go into the Promised Land because of unbelief. Later, both temples were destroyed on the 9th of Av, as well as many, many other calamities down through the centuries.