Today, Turenne, in the Corrèze, is a small, picturesque village that is home to just over 800 inhabitants. For centuries, however, it was the seat of the  last independent fiefdom in France – and immensely powerful.

From 984 to 1738, the Viscounts who ruled it and its population of around 100,000 – stretching about 50km in every direction – were given special privileges allowing them to make their own laws, mint their own money, raise an army and collect taxes, without having to give any to the royal family.

The ...