1147- A fast-day was observed by the Jewish community of Cologne, Germany, in commemoration of anti-Jewish violence and massacre during the Second Crusade.
1556- Portuguese Marranos who had reverted back to Judaism were burned to death in Ancona, Italy.
1906- A devastating earthquake struck San Francisco, followed by destructive fires; estimates of the final death toll were more than 3,600.
May 1, 1921- Arab mobs attacked Jewish residents of Jaffa and stormed the Zionist Immigration Center, killing 47 Jews. The Arabs used rioting as a political tool: After each outbreak, a British commission of inquiry would pin the cause of the violence on the Arabs' fear of being displaced by Jews. To stop the rioting, the commission would recommend that restrictions be placed on Jewish immigration. In this particular case, the Arabs won the battle -- to scare the Jews out of Jaffa -- but lost the war: The riots spurred Jewish settlement in neighboring Tel Aviv, which left Jaffa nearly devoid of Jewish commercial interests. Again in 1929, rioting caused Jews to leave Jaffa, and before long Tel Aviv had overshadowed Jaffa as Israel's main commercial center.