Cardinal Richelieu and the Making of France by Anthony Levi — the best English-language biography of the man who built Richelieu. Covers his political career and cultural ambitions, including the town project, in readable depth.
Michelin Green Guide: Châteaux de la Loire — the standard reference for the Loire Valley, with good coverage of Richelieu and the surrounding region. Practical and authoritative on the architecture and history.
Wolf Hall by Hilary Mantel — set in the Tudor court rather than France, but Mantel captures the world of early modern statecraft — the calculations of power, the architecture of influence — that shaped figures like Richelieu. Reading it before or after visiting gives the Cardinal's planned town a richer context.
The Gardens of Versailles by Georges Farhat and Kenneth Woodbridge's Landscape and Antiquity: Aspects of English Culture at Stourhead 1718–1838 — for readers interested in the formal French garden tradition that shaped the Richelieu park. Woodbridge in particular traces the intellectual history of the geometric garden from Versailles outward.