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 1567, under French king Charles IX, the fortifications were strengthened by the construction of a bastioned citadel built around the castle. Following to Spanish attack in 1596, King Henri IV ordered his military engineer Jean Errard'to strengthen the fortifications of Montreuil. 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.
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.
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. 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 is normally open in the summer months, with a small entrance fee.References:
From its origin as a small stronghold built by the ancient Illyrian tribe Dalmatae, becoming a royal castle that was the seat of many Croatian kings, to its final development as a large fortress during the Ottoman wars in Europe, Klis Fortress has guarded the frontier, being lost and re-conquered several times. Due to its location on a pass that separates the mountains Mosor and Kozjak, the fortress served as a major source of defense in Dalmatia, especially against the Ottoman advance, and has been a key crossroad between the Mediterranean belt and the Balkan rear.
Since Duke Mislav of the Duchy of Croatia made Klis Fortress the seat of his throne in the middle of the 9th century, the fortress served as the seat of many Croatia"s rulers. The reign of his successor, Duke Trpimir I, the founder of the Croatian royal House of Trpimirović, is significant for spreading Christianity in the Duchy of Croatia. He largely expanded the Klis Fortress, and in Rižinice, in the valley under the fortress, he built a church and the first Benedictine monastery in Croatia. During the reign of the first Croatian king, Tomislav, Klis and Biograd na Moru were his chief residences.
In March 1242 at Klis Fortress, Tatars who were a constituent segment of the Mongol army under the leadership of Kadan suffered a major defeat while in pursuit of the Hungarian army led by King Béla IV. After their defeat by Croatian forces, the Mongols retreated, and Béla IV rewarded many Croatian towns and nobles with 'substantial riches'. During the Late Middle Ages, the fortress was governed by Croatian nobility, amongst whom Paul I Šubić of Bribir was the most significant. During his reign, the House of Šubić controlled most of modern-day Croatia and Bosnia. Excluding the brief possession by the forces of Bosnian King, Tvrtko I, the fortress remained in Hungaro-Croatian hands for the next several hundred years, until the 16th century.
Klis Fortress is probably best known for its defense against the Ottoman invasion of Europe in the early 16th century. Croatian captain Petar Kružić led the defense of the fortress against a Turkish invasion and siege that lasted for more than two and a half decades. During this defense, as Kružić and his soldiers fought without allies against the Turks, the military faction of Uskoks was formed, which later became famous as an elite Croatian militant sect. Ultimately, the defenders were defeated and the fortress was occupied by the Ottomans in 1537. After more than a century under Ottoman rule, in 1669, Klis Fortress was besieged and seized by the Republic of Venice, thus moving the border between Christian and Muslim Europe further east and helping to contribute to the decline of the Ottoman Empire. The Venetians restored and enlarged the fortress, but it was taken by the Austrians after Napoleon extinguished the republic itself in 1797. Today, Klis Fortress contains a museum where visitors to this historic military structure can see an array of arms, armor, and traditional uniforms.