What is an interesting fact of history that most people don't know about?

During the Spanish Succession War, prostitutes in Madrid, like most of the city, were sympathizers of the candidate for the throne Felipe V de Borbon.

So when English and Portuguese troops arrived in the city to crown Archduke Charles as Charles III in 1706, the prostitutes devised a biological attack on the troops. In collaboration with some doctors, they fixed and perfumed sick prostitutes. Within a month there were 6,000 cases of syphilis and gonorrhoea among English soldiers, enemies of Philip V.