The Mont de Watten stands at the western end of a line of low hills that runs across Flanders. Although it is not particularly high, the flatness of the surrounding land has made it an important strategic location. The hill stands on the right bank of the river Aa, between St Omer and Gravelines.
The river runs through a narrow stretch of marshy ground between the Mont de Watten and the hills to the west. The Romans recognised the importance and made a camp on the hill, protecting the road between Cassel and Boulogne. The village of Watten (meaning "ford" in Flemish) grew up next to the river in the middle ages, but was never very large. Up to this point, houses were not built in the valley because the sea flooded it in bad weather. In the 11th century an abbey was built on the hill.
In 1625 Duchess Isabella, governess of the Spanish Netherlands, inspected Watten with a view to building a fortification there. It is unclear what came of these proposals, but it seems likely that the abbey and a farm on the far side of the valley, the Maison Bleue, were fortified in some way.
In 1638 the French laid siege to nearby St Omer, capturing Watten and including it in their siegeworks. A Spanish relief force arrived and retook Watten from the French after heavy fighting, in which the attack was led by the erstewhile garrison (which had recently been evicted by the French). The Spanish then constructed a dike across the valley at Watten.
This dike caused the river Aa to flood, resulting in inundations'that destroyed the French siegeworks. The French forces withdrew and St Omer was saved.
The Spanish, recognising the strategic importance of Watten for the defence of St Omer, strengthened the fortifications and reinforced the garrison. However, the French returned in 1643 and captured Watten, using it as a base to raid the surrounding countryside.
This French occupation was short-lived and Watten was retaken by the Spanish shortly afterwards. In 1644 just weeks after the successful conclusion of the siege of Gravelines, a French force under Maréchal de Gassion marched from Gravelines to Watten. A few days after their arrival, the French troops carried the main fort by assault, consolidating their position by taking some outlying works over the following days.
In 1644 the fortifications of Watten consisted of a fort on top of the hill (known as the Fort de Watten) and the ramparts of the village, on the right bank of the river. These two main works were supported by a number of outlying forts and redoubts'that protected important approaches.
The main fort on the top of the hill took the form of a pentagon with five bastions, surrounding the abbey. It was an earthwork with a dry ditch'and a covered way. The bastions were of a slightly irregular form, especially the Bastion d'Elboeuf in the west (towards the village), which had a very narrow gorge.
There was a demi-lune'at the eastern entrance (where the approach was flat, not uphill as on the other sides) and an offset demi-lune on the south side of the Bastion d'Elboeuf. The weakness of the main fort was its inability to dominate the valley below.
Although it is considerably higher than the village, it is impossible to see even the top of the church tower from the west bastion of the fort due to the slope of the hill. This deficiency meant that several hornwork-like projections had to be added to the covered way to extend the vision and range of the fort.
There were two of these projections to the west, looking out over the river, one to the north and one to the south. These works gave the garrison a more adequate view of the surroundings, but it was still necessary to build outlying works to control the river.
The outlying fortifications were small, but they protected key locations in the river valley. Firstly, the village of Watten itself was fortified with a roughly angular trace.
The ramparts were earthworks and they formed a demi-bastioned'front to the north and the south and a redan'to the east (facing up the hill towards the main fort). To the west, the village was protected by a channel of the river. On the far side of the channel, on an island in the river, there was a demi-lune.
In addition, a demi-bastioned front ran across the village, entrenching the church, which was slightly uphill, against the lower part of the village. These fortifications were not substantial, but their purpose was not so much to resist a prolonged siege but to prevent an attacker from overrunning the village with an infantry assault.
Another key outlying work was the Wattendam Fort. This fort, a simple affair with two bastions and a demi-lune in its rear, straddled a channel of the river. This fort protected sluices that were important for controlling the flow of the river water.
When the French captured Watten in 1644, they strengthened the upper fort by building a hornwork'on the eastern side in front of the Porte de Cassel, where an attack was most likely. They also planned to build a large fort with 4 or 5 bastions in the valley, but in the end it was decided that the ground was too wet.
Instead they build some extra redoubts and constructed a line between the upper fort and the village and another line stretching south-west from the fort. These works gave the garrison a better view over the valley and allowed more communication.
Apart from the larger works, there were three square redoubts at Watten. The largest was the Redoute du Moulin, built around a windmill on a small height between the village and the Wattendam Fort.
To the north, another redoubt called the Fort de Ruth stood next to the river Aa, guarding against an attack from the north. The smallest redoubt was the Redoute de la Digue, to the west of the village, which protected the western end of the dike.
To the east of the main fort, the French built lines of pallisades as a form of temporary entrenched camp, where a force of 10,000 men could camp just outside the fortifications.
This camp was used in 1645 when the Spanish garrison in St Omer made plans to retake Watten, but in the end they did not attack. In 1646, seeing the garrison was weak, the Spanish again tried to capture Watten, but Gassion stopped them at Cassel.
The finally succeeded in 1647 and planned to demolish the fortifications. However, either these plans were not carried out or the work was not very thorough, because when Turenne'arrived in 1657 he was able to restore the fortifications without much difficulty.
Watten was returned to Spain by the Treaty of the Pyrenees'in 1659, but the fort gradually declined in importance. At Siege of St Omer in 1677, the French occupied without a fight, which suggests the fortifications had decayed and were less formidable the in 1644.
In 1678 the Treaty of the Nijmegen'made Watten French again. When Vauban'was strengthening the fortifications of St Omer he recognised the importance of Watten for controlling the river and considered strengthening the fortifications there.
However, no work was carried out and the fortifications of Watten were abandoned, although they were briefly reoccupied in 1710, when France was on the defensive in the War of the Spanish Succession, having lost some important nearby fortresses.
In 1735 there was another project to rebuild the fort. This time work was started, but the project was cancelled before much was done. Yet another project to build a fort at Watten was drawn up in the 1880s, but was cancelled due to a lack of funds.
The advantages of controlling the river by fortifying Watten were always offset by the poor field of vision over the valley from the main fort and the lack of natural defences to the east, which was the most likely direction for an attack.
The fortifications of Watten are unusual in France in that they were earthworks that were never revetted in stone. The fortifications in the valley have been swept away by erosion and construction, although the north side of the churchyard still follows the line of the old ramparts.
On the hill, most of the main fort has survived, although the ramparts have suffered from erosion. The most impressive part is the Bastion d'Elboeuf, complete with a stone mindmill, which was built in the 18th century to replace a wooden mill that stood there in the 17th century.
Today, there is a path leading up from behind the church to the remains of the main fort, with information panels about the site. Unfortunately, the abbey tower is private property, so it cannot normally be visited but is open on special occasions.
The train station Watten-Eperleques is on the other side of the river from the centre of the village, a short walk from the main fort. There is a tourist information office in that can provide information about the Watten and the surrounding area.