In medieval times the town of Montreuil-sur-Mer stood on a hill near the mouth of the river Canche. An important port, it was first fortified in the 9th century, when a stone wall was built around the town.
In the 13th century the town was expanding and so new walls were built to enclose it. The new circuit of defences extended farther south to take in a new market square and farther east and north down the hill to take in the lower town, which was growing up on the riverbank. At the north-east corner of the town a castle with 8 towers was built, forming part of the walls. However, Montreuil's fortunes declined as the estuary silted up and much of the lower town was not built up.
In the 16th century the town was on the northern frontier of France, with the Imperial province of Artois just to the north. Montreuil saw several sieges in the wars between the French and the Habsburgs and their English allies. The first came in 1522, when a joint Imperial and English force failed to capture the town. The second, in 1537, was more disastrous. This time the besiegers captured the town and burnt it, destroying many of the houses.
As a result, the French decided to strengthen the fortifications. The work was carried out by an engineer called Jean Marin. Marin saw that the weakest part of the town was the north and east sides where the walls were at the bottom of the hill rather than at the top. He built a new rampart in the north and east, inside the old walls. The result was an inner circuit enclosing the upper town.
The new wall had 5 bastions', which were among the first to be built in France. Below them, the 13-century walls around the lower town were left in place to serve as an outer line of defence.
When the English laid siege to Montreuil in 1544, the work on the new fortifications was sufficiently advanced to deter them from attacking from the north or the east. Instead, they attacked from the south, where the approach is less steep, but they were unsuccessful.
After holding out for 3 months, Montreuil was relieved by a large French army that forced the English to retreat to Boulogne. Work on the fortifications continued and was completed in 1549.
In 1554, Emporer Charles V'started building a fortress at Hesdin, just 18 miles (30km) up the river from Montreuil. France was frequently at war with the Habsburgs and later the Spanish, so Montreuil remained an important frontier fortress.
In 1567, under French king Charles IX, the fortifications were strengthened by the construction of a bastioned citadel'built around the castle. The citadel had five irregular bastions, two demi-bastions'facing into the town and three full bastions facing the countryside.
There was an gate leading into the town (the Porte de la Citadelle), made in the curtain between the two demi-bastions, and another gate leading out into the countryside (the Porte de Secours). This second gate was made in the right flank of a bastion, a common configuration in the 16th century.
In 1596 the Spanish captured Calais and Ardres, taking Amiens the following year. Following this setback, King Henri IV ordered his military engineer Jean Errard'to strengthen the fortifications of Montreuil, which could well have been the next target for the Spanish.
Between 1597 and 1605 Errard improved the defences in various places, building a hornwork'in the south, where the English had attacked in 1544. He also realigned the trace of the citadel, which had been rather poorly laid out.
To flank the stretch of wall leading along the western side of the town, Errard built the large Bastion de Bouillon, named after Maréchal de Bouillon, who was the governor of Picardy at the time.
This bastion had to be built at a lower level to the 13th-century walls, since they run along the top of a steep slope at this point. The Bastion de Bouillon has its flanks at right angles to the faces, as proposed in Errard's treatises on fortification.
Finally, the 13th-century wall around the lower town was reinforced by the construction of 3 demi-lunes. Thus, in the early 17th century Montreuil was protected on all sides by artillery fortifications.
Monrtreuil was again strengthened in the 1630s when Chevalier de Ville, Louis XIII's military engineer, had the walls backed with earth to enable them to absorb cannon-fire more effectively. The old round towers were lowered and adapted for artillery and muskets.
De Ville also built a second hornwork, known as Fort Louis, in the south in front of the one built by Errard. Its purpose was to add more depth to the defences in the south, where the hillside is least steep.
Although Montreuil was left in peace after the siege of 1544, it remained on the frontier until the Treaty of the Pyrenees'in 1659, which gave France the province of Artois, including the fortresses of Arras, Gravelines and the smaller fortress of St Venant.
This left Montreuil some distance behind the frontier, but still the only large French fortress town in the gap between Arras and Gravelines, facing the Spanish fortresses of St Omer and Aire-sur-la-Lys.
Vauban'visited Montreuil twice in the 1670s to survey the fotifications. He disapproved of the citadel and even suggested demolishing it and building a bastioned front in its place. In the end he added a demi-lune to the town side instead.
Vauban was also responsible for three earthwork demi-lunes on the east side of the upper town and for the covered way'surrounding the defences. Finally, he put sluice gates in place for inundations'and built three bastions and a hornwork to the north of the lower town.
However, the steady French advance northward eventually relegated Montreuil to the status of a rear place. In 1678, the Treaty of Nijmegen'moved the frontier even farther north and provided France with a host of new fortresses, but the town's proximity to the coast ensured its continued importance.
The coast between Calais and Boulogne was vulnerable to attack (as was demonstrated in 1544) and within easy reach of England, a naval power that was frequently at war with France. The necessity of guarding against an attack from the sea, which would bypass the fortresses to the north, persuaded the French to maintain the fortress of Montreuil.
Montreuil was garrisoned throughout the 18th century but the fortress did not see any action after 1544. In the first half of the 19th century the Porte de Boulogne, the northern entrance to the upper town, was rebuilt to improve access.
In 1845 the north bastion of the citadel was rebuilt with Haxo casemates and in 1867. The fortifications of the town were declassified, but the citadel was garrisoned until 1929.
Although the fortifications of Montreuil were declassified in the mid-19th century, little demolition work was carried out, with the result that most of the defences have survived intact. Among the exceptions are the two hornworks in the south were removed (although a section of Errard's hornwork has survived) and Vauban's bastioned works to the north of the lower town, which were levelled to make way for the train station.
For the most part the fortifications are in good condition, although the earthwork demi-lunes on the east side of the upper town are rather overgrown. The citadel, which is currently being restored (Jan 2009) is normally open in the summer months, with a small entrance fee.
The Tourist Information Office can provide a map of the town, showing the various walking routes round the fortifications, along with some literature on the history of Montreuil. The station is just north of the old town and is served by trains on the Lille-Boulogne line.
The fortifications of Montreuil-sur-Mer are a rare example of French 16th-century bastioned works that were not heavily altered by later engineers. The ramparts make an excellent visit and offer fantastic views of the countryside.