Mont-Dauphin is one of the many places fortified by Vauban in the second half of the 17th century. Following invasions of Provence by Savoy in 1691 and 1692, Louis XIV dispached Vauban to put the frontier in a better state of defence. In 1692 he came to the Plateau de Mille-Aures, which overlooks both of the invasion routes used by the Savoyards, to fortify it.
The ground in question was on a high hill, roughly four-sided and only readily accessible on one side, another side being steep but passable and the further two sides being cliffs. This meant that the place would only require a short amount of bastioned front, the remainder only requiring a basic wall. The plateau was previously uninhabited, so it was decided that a new town would be built within the fortifications. Plans were made for a front of three arrow headed bastions and two demi-lunes in the north, where the defences were most approachable.
To the south, Vauban planned a trace of smaller bastions, this approach being all but inaccessable. The entrance here was carried over a small demi-lune. Later in the 18th century, the trace of the southern defences was altered, but this demi-lune remained, leaving it oddly skew from the wall. There were serious problems obtaining enough stone for revetting the ditches and ramparts. Thirdly, the threat of invasion from Savoy subsided before the fortifications were completed and the fortress lost its immediate importance. Despite this, Mont-Dauphin was strengthened after French troops suffered a defeat nearby in 1745. For the rest of the century, the barrack buildings multiplied, but some elaborate and extensive plans for extra layers of defence drawn up in 1747 were shelved.
One of the additions that was actually realised is a lunette called the lunette d'arçon, which is an advanced work in the north, but is connected to the fortress by an underground passage. The fortifications at Mont-Dauphin are in very good condition.
In 2008, the place forte of Mont-Dauphin, was listed as a UNESCO World Heritage Site, as part of the 'Fortifications of Vauban' group.
References:Celje Castle was once the largest fortification on Slovenian territory. The first fortified building on the site (a Romanesque palace) was built in the first half of the 13th century by the Counts of Heunburg from Carinthia on the stony outcrop on the western side of the ridge where the castle stands. It had five sides, or four plus the southern side, which was a natural defence. The first written records of the castle date back to between 1125 and 1137; it was probably built by Count Gunter. In the western section of the castle, there was a building with several floors. Remains of the walls of this palatium have survived. In the eastern section, there was an enclosed courtyard with large water reservoirs. The eastern wall, which protects the castle from its most exposed side, was around three metres thicker than the rest of the curtain wall. The wall was topped with a parapet and protected walkway.