18 June 1822,
Denmark Vesey and other citizens preparing the slave uprising were arrested in South Carolina, United States. Denmark Vesey was not a slave, he was a free citizen. In the city of Charleston, thousands of black citizens already involved in the manufacture of weapons accused him of wanting to set the city on fire and starting a slave revolt.
At that time it was the sixth largest city in the United States. Someone reported them and the authorities hanged 35 people.
Source:
Howard Zinn, A People's History of the United States.