In 1631, to thank his minister, Cardinal Richelieu, for his eminent services, King Louis XIII did him the favor of erecting "a town enclosed by walls and moats and building a market hall" and establishing four annual fairs and two markets per week. Thus emerged from nothing, an "ideal city" according to the precepts of the time which would bear the name of the Cardinal. Richelieu entrusted Jacques Lemercier, architect of the king, author of the Sorbonne and the Palais-Royal, with the task of building, on the site of the family property, a vast castle, a reflection of his grandeur and a new city, nearby. Nearly 2000 workers would work on the site. Inside the walls, the Cardinal gave the land to whoever agreed to build a pavilion within two years according to the plans filed with the city registry. The inhabitants will be exempt from tax and gabelle until there are 100 houses built. 4/5 of the project will be completed between 1632 and 1642, the year of the Cardinal's death. Contrary to the words of Jean de la Fontaine (who also ironically described the town as "the most beautiful village in the universe"), far from being deserted, the town had 4,000 inhabitants in 1690, compared to less than 2,000 today.
This innovative project, which linked the construction of a castle and a town in the same program, foreshadowed the Versailles construction site that would open 30 years after the completion of the city walls of Richelieu. Adjacent to the walls, Richelieu Park, with an area of 475 ha, housed the vast estate of the castle of the du Plessis family (original surname of Cardinal Richelieu), of which only a few vestiges remain today.
Richelieu is now a somewhat unusual town in the French landscape, with its three access gates and its two large symmetrical squares. Organized in quadrilaterals and perpendicular streets in the manner of American cities, it offers a unique testimony to urban planning of the Grand Siècle.