Our story began in 1223 when king Louis VIII gave county of Boulogne, Aumale and Domfront to his half-brother Philip Hurepel, count of Boulogne. This one immediately raised a castle and its surrounding wall on a place that used to be occupy by Romans. Well, he had to establish his new power! Hurepel also raised a fortress in Calais and in Hardelot.
The building site in Boulogne began in 1230. We had here a keepless castle, typical of the 13th century: did you know this particularity came from the Orient? At that time, it was brand new in Western Europe! On the contrary, Calais castle founded in 1228 by Hurepel had a keep, like all medieval fortresses.
Boulogne stronghold was preserved during Hundred Years War, but artillery technical was more and more perfect... so from 1515 to 1544, they reinforced the defensive system, adding an armour plate on the wall. Anyway, the castle fell to the English in 1544: Henri VIII of England continued the building site then the French came and get back the stronghold (thanks to king of France Henri II and his treaty of Outre-Eau, in 1550!). These one completed the fortress in 1565.
Louis XIV found a damaged stronghold: he didn't want to spend money in big restorations, so he decided to demolish it! Oh, a pretty radical solution! Remaining buildings were transformed into barracks in the 18th and 19th centuries. Did you know that in 1840, they locked here the future emperor Napoleon III, after his coup d'Etat attempt (failed!) in August 1840?