In April 1721, a smallpox outbreak swept through Boston. This was the latest in a string of six epidemics that had, since, 1630, laid waste to the city. Cotton Mather, a local slave owner and preacher, claimed to be in possession of a way of preventing contraction of the disease. Mather, who had first come to public prominence as one of the thinkers behind the Salem Witch Trials, had gotten the method from one of his former slaves.