I think Louis XVI and Marie Antoinette should have been killed in the French Revolution. The royal couple had to move out of the castle because of a mob that marched Versailles. In August 1792 they were arrested by the sans-culottes. In September the monarchy was abolished by the national convention. In November evidence of Louis XVI counter revolutionary intrigues with Austria and other foreign nations. Marie Antoinette was later found guilty of treason and was put to death
