Signs posted throughout Philadelphia on May 15 warned that “a convention to effect the immediate emancipation of the slaves throughout the country is in session in the city, and it is the duty of citizens who entertain a proper respect for the Constitution of the Union and the right of property to interfere.”

More than three thousand reformers gathered at the newly dedicated Pennsylvania Hall the next day as a hostile crowd formed outside. Among the speakers was Angelina Grimké Weld. She and her sister Sarah, the daughters of a wealthy South Carolina plantation owner, were famous in the North for their antislavery lectures. Just two days before, Angelina had married the abolitionist Theodore Weld in an interracial ceremony.

“I have seen it! I have seen it!” Mrs. Weld told the convention. “I know it has horrors that can never be described. I was brought up under its wing. I witnessed for many years its demoralizing influences and destructiveness to human happiness.” As she spoke, stones crashed through the windows. “What is a mob? What would the breaking of every window be? Any evidence that we are wrong, or that slavery is a good and wholesome institution?”

Though the evening passed without further violence, the same mob gathered the next day as the feminist Lucretia Mott and others addressed the convenion. That night the mob set fire to Pennsylvania Hall, burning it to the ground.