Dunkirk Town Fortifications
The main walls of Vauban's fortress of Dunkirk were based on the Spanish fortifications constructed in the 1640s. The Spanish trace was formed of 10 bastions in an oval shape surrounding the town, with its medieval walls, and the harbour. By the time the French came into possession of Dunkirk in 1662 there were a number of demi-lunes and a covered way, but most of the outworks were probably still made of earth.
Vauban left the existing bastions mostly as they were, but extensively remodelled the outworks. He moved the demi-lunes further from the main wall, widening the ditch and building a strong covered way. The south-east section of the defences was strengthened even more by a second covered way and a hornwork flanked by two lunettes.
The most vulnerable part of the town's defences was the point where the walls met the harbour mouth. At this point, known as the Tête de Nieuport, an enemy could make use of the sand dunes to move along the shore without being seen from the walls. To offset this weakness, there were extensive cavaliers (extra tiers of guns) on top of the three bastions closest to the dunes. These bastions were also protected by two false brays. The central of these three bastions, the Bastion du Château had a lunette in front of it. The dunes themselves were covered by the Fort de Revers.
The east gate of Dunkirk, called the Porte de Nieuport, was protected by a double demi-lune and the hornwork. To enter by this gate travellers had to cross four bridges over the flooded ditches. This sector of the defences faced ground that was relatively dry and faced towards the frontier (away from France). For these reasons, the area would have made a good approach for an attacking army, which no doubt caused Vauban to add these extra layers of defences.
On the south side of the town stood the main entrance to the fortress, the Porte Royale. This so-called royal gate was embellished with architectural decorations, since it was the gate that the king and other important visitors from Paris were most likely to use. As with the Porte de Nieuport, the Porte Royale was protected by a double demi-lune. There were two guardhouses half-way along the bridge to the gate itself, so that traffic into and out of the fortress could be controlled by the garrison.
Either side of the Porte Royale were two water gates, arches in the wall through which waterways entered the town. These were the Canal de Furnes from the east and the Canal de Bergues from the south. The canals were important for navigation and for maintaining the water level in the flooded ditches around the fortifications. Where the canals crossed a ditch, there was a specical dam, called a "bartardeau" on both sides. The batardeaux had sluice gates which allowed the water levels in the ditches to be controlled. The bartardeaux effectively created bridges across the ditches, so they had a sharp ridge along the top to prevent an attacker from using them to reach the walls. In the centre of each batardeau was a "dame", a wide round pillar that formed a barrier to anyone trying to cross it.
Before entering the town, the two canals ran parallel for a short distance. The ground between the canals was the site of an advanced covered way and an earthwork defence line. Outer layers of defences and isolated outworks like this were a feature of Dunkirk's fortifications. The goal was to protect key waterways and delay the enemy as much as possible during a siege.
Inside the town itself, the old medieval walls on the landward side were demolished to make room for more houses. Next to the harbour the medieval wall was left in place, perhaps so that traffic to and from the quays would have to pass through the gates and could be controlled more easily.
At the edges of the town, just behind the ramparts, a series of barrack buildings were construced. The barracks provided permanent accommodation for the garrison, which had previously been billeted with the townspeople. Their location close to the walls meant that the soldiers could be deployed quickly in case of an attack. Similarly, many of the bastions were equipped with their own small gunpowder magazine. In a large fortress like Dunkirk the distance to the main magazine could be significant, so these so-called "ready magazines" were a way of safely storing the powder close to where it was needed.