The principality was created by Napoleon for his chief diplomat Charles Maurice de Talleyrand-Périgord. It was nominally sovereign, but the prince did have to take an oath to the king.
The principality was short-lived. Talleyrand was never to settle down and actually rule his new principality.[1] In 1815, after the Napoleonic Wars, the town was ceded back to the Papal States.
In 1860, it joined Pontecorvo, the other southern Italian papal exclave, in being united with the new Kingdom of Italy.