Vernon extends at the border between the Duchy of Normandy and the rest of the Kingdom of France. It was of strategic interest for both England and France during the Middle Ages. From the 10th century, a bridge and the first fortifications were erected in Vernon. In the 12th century, King Philippe Auguste kept fortifying the town and built a small castle on the right bank of the Seine and a fortified one on the left bank, whose Tour des Archives culminates at 72 ft (22 m). Vernon definitely became French again after the Count of Dunois liberated the town in 1449.