This date (April 21) in history:
in 1506 – The three-day Lisbon Massacre comes to an end with the slaughter of over 1,900 suspected Jews by Portuguese Catholics.
The Lisbon Massacre, alternatively known as the Lisbon Pogrom or the 1506 Easter Slaughter was an incident in April, 1506, in Lisbon, Portugal in which a crowd of Catholics, as well as foreign sailors who were anchored in the Tagus, persecuted, tortured, killed, and burnt at the stake hundreds of people who were accused of being Jews and, thus, guilty of deicide and heresy. This incident took place thirty years before the establishment of the Inquisition in Portugal and nine years after the Jews were forced to convert to Roman Catholicism in 1497, during the reign of King Manuel I.
for more info, go to wikipedia: http://en.wikipedia.org/wiki/Lisbon_Massacre