In the Narrow Places: An 18 Tammuz Text Study WexCoComm July 18/18 Tammuz

(6) The mishna discusses the five major communal fast days. Five calamitous matters occurred to our forefathers on the seventeenth of Tammuz, and five other disasters happened on the Ninth of Av. On the seventeenth of Tammuz the tablets were broken by Moses when he saw that the Jews had made the golden calf; the daily offering was nullified by the Roman authorities and was never sacrificed again; the city walls of Jerusalem were breached; the general Apostemos publicly burned a Torah scroll; and Manasseh placed an idol in the Sanctuary. On the Ninth of Av it was decreed upon our ancestors that they would all die in the wilderness and not enter Eretz Yisrael; and the Temple was destroyed the first time, in the days of Nebuchadnezzar, and the second time, by the Romans; and Beitar was captured; and the city of Jerusalem was plowed, as a sign that it would never be rebuilt. Not only does one fast on the Ninth of Av, but from when the month of Av begins, one decreases acts of rejoicing.