Late on the night of 20 June 1791, a compact but heavily-laden coach rumbled out of the Tuileries Palace. It was bound for the royalist-held fortress of Montmédy, some 150 miles away on France’s northeastern frontier. For those aboard – King Louis XVI, his consort, Marie-Antoinette, and the royal children, all disguised as humble members of the bourgeoisie – it was a bid for freedom: escape from the revolutionaries who had dismantled France’s traditional royal government over the previous two years and reduced the royal family to de facto captivity.

Just as they neared their destination, however, things went wrong. Recognised en route, the party was arrested by partisans of the revolution at Varennes-en-Argonne, just thirty miles short of the border. The National Assembly – the new revolutionary legislature – dispatched a three-man delegation to escort the escapees back to an outraged Paris.

On that return journey, one of the National Assembly’s delegates, a slim, charming, 29-year-old lawyer from Grenoble, fastidiously dressed à la mode anglaise, had the presumption to take a seat in the carriage with the king and queen. He was Antoine Barnave, one of the most influential politicians