The castle was built at the estuary of the Seine River, where it narrows into a river rather than a bay inlet. One side fronted the river, elevated by a cliff. The defenses were focused on the other sides. This old drawing of the castle’s cliff side shows why.
The castle was built in a narrow triangle, with a tower facing the sea, at the “needle.” The tower that is now there may have been built later, but the original gatehouse facing the city, and two towers/gates on the most heavily fortified short side of the triangle, are the original works from the 1200s.
The gatehouse now has glass windows, but these would originally have been perches for archers. Close to the ground level, the only slits in the walls are extremely narrow ones just for archers. Each story above ground level, the windows get a little bit larger, as the likelihood of attack through them drops off.
Inside the original bailey, a large house was constructed in the 18th century. But behind it, you can still see older sections. Look in the background of this photo for striped stonework that was typical of Romanesque churches, built in the pre-Gothic period.
To each side of the gatehouse, the ruined wall is clearly 13th century provenance, with round towers spaced periodically for defense. At the heavily defended end, the towers are wide and very round, a clear late-13th century marker. Later buildings were added after the walls were no longer used for defense, but you can still see the original towers.
The Chateau has its own Facebook page.