In 1600, The 8th Baron Mountjoy was sent to the Kingdom of Ireland as the last Lord Deputy of Queen Elizabeth I. He joined a group of mercenaries who had been fighting in the valley of the Blackwater. Lord Mountjoy came to the place now known as Charlemont where he established a bridge of wood and a fort to guard the bridge in 1602. Prior to his founding of Charlemont Fort, the place had been called "Achadh an Dá Chora", the 'Field of the Two Weirs', but it was renamed in his honour using his name and the French word for hill, 'Mont', i.e. Charlemont.