From Wikipedia...

The importance of Chinon derives from its position on the bank of the Vienne river in Chinon, France just before it joins the Loire. From prehistoric times, the rivers of France formed the major trade routes, and the Vienne joins the fertile southern plains of the Poitou and the city of Limoges to the thoroughfare of the Loire, thus giving access to the sea at the port of Nantes on the western coast, and to the Île-de-France in the east.

The chateau was a residence of Charles VII, the Dauphin of France in the early 15th century, when Touraine was virtually the only territory left to him in France, the rest being occupied by the Burgundians or the English. Joan of Arc arrived at the castle, at the beginning of her quest to liberate France from the English on March 8, 1429; it was here that she recognized the disguised Dauphin from amongst his courtiers, a feat which helped to persuade him to accede to her urging to declare himself king and raise an army to liberate France.