The castle was built in the 13th century by Philippe Hurepel (1180-1234), count of Boulogne and son of Philip II of France.
The castle is built in the eastern corner of the medieval walls surrounding the Haute Ville (literally, high town - the part of Bologne on the hill).
The remains of Château de Hardelot in nearby Condette show that Hurepel used this design for at least one other castle.
[1] The Château de Boulogne-sur-Mer is built on a flat terrain and falls under the category of court castles.
After passing the main entrance, which has lost its original drawbridge, the first building on the left is what was the state room back when the castle was built, then follow the chapel, the armoury, the lodgings, and the kitchens.
In the sixteenth century, on the eastern side of the castle, the walls were embedded in thick stone masonry in order to form a shielding plate, and faussebrayes were built to encompass five of the nine towers under an almost continuous roof in order to protect the castle from the ever advancing artillery at the time.
It is pierced by three levels of arrowslits constructed in staggered rows and covered with a conical roof (toit en poivrière in French).