In the 10th century, the fortress was held by high officials of the Carolingian kings, the Counts of Blois.
One of them, Theobald "the Cheat", became a count around 942 and remained so until 974. His rapid social rise no doubt aroused jealousy and motivated the appearance of this unflattering nickname. Theobald the Cheat was politically clever. He considerably increased the possessions of the counts of Blois. Their territorial domination extended from the gates of Paris to the south of the Loire. Theobald had powerful tower residences built on his territory, notably in Chartres and Châteaudun. In Chinon, he had a stone tower built in 954 to reactivate the defensive capacity of the site, especially against the Vikings who were moving up the Loire.