On April 19th, 1506, an anti-Semitic riot broke out in Lisbon, Portugal, led by Dominican priests shouting, ‘Death to the Jews!’ Churchgoers who followed the fanatical clergymen through the city ended up murdering some 2,000 New Christians – Portuguese Jews who’d been forcibly baptised in a mass conversion nine years earlier. Their bodies were dragged to the main square and burnt in two huge pyres. I discovered this crime against humanity in 1990, while researching daily life in Lisbon during the Age of Exploration, but when I asked my Portuguese friends what they knew about the massacre, they all replied,...