Tisha Be'av, which began last night, is the ninth day of the Hebrew month of Av. On it we commemorate the destruction of the First and Second Temples in Jerusalem, in 586 BCE and 70 CE, respectively, and the expulsion of the Jewish people from Israel. Along with Yom Hashoah and Remembrance Day, Tisha Be'av is one of the most melancholy days in the Jewish calendar. Beyond the destruction of the two Temples, the Ninth of Av has the distinction of being inauspicious in other ways. On that date: In 1096, the First Crusade began, destroying Jewish communities in Europe. In 1290, the Jews were expelled from England, and, in 1306, from France. In 1492, the Jews were thrown out of Spain. In 1648, thousands of Polish Jews were murdered in the Chmielnicki massacres. In 1882, pogroms swept Russia. In 1914, World War I broke out. In 1942, Herman Goering's letter charging Reinhard Heydrich to prepare "the complete solution of the Jewish question" was issued on the eve of the eighth of Av. Today we cannot but also reflect upon the existential threats facing the Jewish state. THE DAY is traditionally marked by fasting and recitation of the Book of Lamentations, the Prophet Jeremiah's heart-wrenching narrative of Jerusalem's fall: O how the city once so populous Remained lonely like a widow! She that was great among nations, A princess among the provinces, Has become a tributary. BEYOND THE sacred and historical significance of Tisha Be'av, the day is replete with contemporary relevance. Our attention is called to the Temple Mount, which, hundreds of years before Muhammad was born or Jesus preached, was the epicenter of Jewish civilization. Too bad, then, that even relatively moderate Palestinian leaders such as Mahmoud Abbas and Ahmed Qurei will not acknowledge the Jews' ancient link to this place. Their refusal makes efforts to reach an accommodation immeasurably more complicated. Most relevant of all is how we Jews behave toward one another. A minority in the settler movement have chosen to conflate the uprooting of 8,500 Jews from Gaza and northern Samaria during the disengagement with the Jewish loss of sovereignty in ancient Israel and the ensuing 2,000 years of exile. This newspaper is sensitive to the spiritual suffering of those who lost their homes and communities in the summer of 2005, only to see them turned into launching pads for attacks against Israel. Yet to draw a parallel between the decision of sovereign Israel to relocate its citizens from Gaza to elsewhere inside the country and the Roman expulsion of the Jews from the Land of Israel is inexcusable, arrogant and simply wrongheaded. Just as elements on the Left co-opted Yitzhak Rabin's memory and made approval of his Oslo policies synonymous with a desire for peace, some on the Right have made opposition to disengagement a litmus test of Jewish fidelity. Isn't it obvious that such closed-mindedness and self-righteousness fosters a disunity that our enemies do not hesitate to exploit? Have we forgotten that even as the Romans massed ominously on the horizon, Jews of the Second Temple period were riven with factionalism, each camp clinging to its false certainties? Unable to put their differences aside, they contributed to the undermining of the Jewish commonwealth. As the historian Josephus records, 1.1 million Jews were killed during the ensuing siege and destruction of Jerusalem. Tens of thousands were taken captive or sold into slavery. SOMETHING remarkable was set to happen last night in Beijing. President Shimon Peres, in China with other world leaders for the Olympics, was to attend Ninth of Av services and participate in reciting from the Book of Lamentations. Even as we mark this day with solemnity, let us not lose sight of how far we have come. Across the millennia of the Jewish people's exile, our ancestors could scarcely bring themselves to dream of a day when the Jewish people would be sovereign again in their beloved Zion - let alone an Israeli team competing in the Olympics in China. This generation has merited witnessing the restoration of Jewish sovereignty in the land, and a thriving capital in Jerusalem. Our political, theological and social differences notwithstanding, we have a responsibility to the generations to cultivate the cohesion upon which the Third Commonwealth depends.