9 Av, the day of mourning commemorating the destruction of the two Temples. 2 Kings 25.8–9 says that the First Temple was burned (by the Babylonians) on 7 Av, while Jer. 52.12 dates it on 10 Av; the Talmud places it on 9 Av. The Second Temple was destroyed (by the Romans) on 10 Av.