Here are a few photos showing what remains of the medieval château-fort at Saint-Aignan-sur-Cher. In the first image, you can see the old stone tower on the right, between the Renaissance château and the big trees on the far right.
According to J.-J. Delorme, author of the book Histoire de la ville de Saint-Aignan (Loir et Cher), the town was likely founded in about the year 970, more than 1100 years ago. The promontory on the south bank of the Cher, where the château stands now, had probably been fortified by the Romans a thousand years earlier, but nothing remains from that period except a section of an old Roman road south of the town. There are more substantial Roman ruins in the nearby town of Thésée.
The tower you see here and the rest of the ruins might have existed as early as the year 800. Then, Saint-Aignan was under the control of the counts of Blois, who also ruled over the old Touraine province to the west. The name of the tower is La Tour Agar — Agar or Agard was an ancient name for this area. Norsemen (Vikings) invaded this part of France around that time — thus the fortifications.
It's a long and complicated history, and the details are hard to pin down. The first church in Saint-Aignan was built during the 10th or 11th century, but the area had already been settled by so-called "hermits" and monks for a long time before that. Wolves and marauders roamed the countryside. Warlords fought over territory.
Ruins such as these attest to this kind of history. The counts of Anjou moved in from the west. Burgundians, the power-holders to the east, took over in the 11th century. It all makes your head spin.