Boisbelle, as the area had formerly been known, had been an allōd under Roman law, a sovereign freehold with none of the constraints of feudal tenure but one wherein the owner had the rights of a ruler and governed the territory in complete independence. Thus, the inhabitants of Boisbelle were free from any taxes or services and could not be conscripted into the armed forces. They were, however, subject to the requirements of the Roman Catholic Church.
In 1605, Maximilien de Béthune, Duke of Sully, a Protestant and a friend of King Henri IV for more than 30 years, bought Boisbelle from the Duke of Nevers. The French Treasury challenged the tax-exempt position of Boisbelle so Sully obtained letters patent from Henri IV in 1606 confirming its status and the immunity of its inhabitants. The dispute continued until 1608 when Henri IV issued further letters declaring the people of Boisbelle free of all tax in perpetuity. Apparently secure, Sully decided to build a new capital, Henrichemont, in honor of the king and the first stone was laid in April 1609.
Then, tragedy! On 14 May 1610, Henri IV was assassinated, Sully lost his friend and protector, his offices and his income. Construction slowed, contractors fell into dispute and lawsuits abounded. In 1624, Sully was ordered by the court to pay the contractors and in 1636 the owners of the few private houses that had been built, all sold at a loss. Ultimately, on 24 September 1766, the 7th Duke of Sully and last independent Prince, ceded the principality to the Crown. It was integrated into France and the inhabitants lost all their privileges. Too bad! Still, it was a nice coffee break and served to confirm that its not what you know but who you know, at least until they are assassinated - see pictures here.