In the 7th century, Benedictine monks founded an abbey on a hill next to the river Aa. The founder, Bishop Omer also founded a religious college and a chapel. A community grew up around the religious institutions, and the marshland around the high ground was cultivated. The town that grew up became known as Saint-Omer and its cloth industry prospered, with trade coming up the river from Gravelines, which became known as 'the port of Saint-Omer'.
After the Normans attacked the town in the 9th century, walls were built to protect it, the abbey having its own walls, forming a citadel. Charles V consolidated the defences, constructing three strong bastions on the western side of the town and a flooded ditch.
Saint-Omer became part of the Spanish Netherlands in 1493 and was made a bishopric in 1553 (about the same time as the defences were improved) and it continued to thrive and grow. Jesuits were trained there including English Catholics, who came secretly to be trained as priests (Catholics were persecuted in England at that time). The French made attempts to capture it in 1551 and 1596 but were defeated.
Two more French attacks (in 1638 and 1647) failed in the face of the difficult marshy terrain and strengthened defences, but the siege of 1677 saw the town finally fall to Louis XIV's unstoppable advance. The town resisted for only 17 days before surrendering.
Later that year Vauban visited the town and inspected the fortifications. He had the ramparts revetted in brick (as at Le Quesnoy and several other northern places) instead of stone, because stone would splinter when hit by cannon shots, sending deadly shards flying and potentially injuring the defenders.
Vauban also added various demi-lunes and counterguards, a hornwork to the west and a covered way extending most of the way around the defences. In addition to the town's defences, there were several outlying fortifications.
As the ground to the east of the town was marshland, houses could only be built alongside the road, which was raised. Thus, Saint-Omer developed some linear suburbs along the roads to the east. In order to protect these, Vauban built three fortifications, the Fort des Moulins and two other detached hornworks.
The fortifications of Saint-Omer were dismantled between 1892 and 1895 but part of the western front centred on St. Venant's bastion was preserved and transformed into public gardens, which were finished in 1897. This section of surviving ramparts includes the large St.Venants bastion (which now has a car park on top), the walls either side of the bastion and one flank of each of the two adjacent bastions.
There is also a tunnel that appears to have given access to the ground floor of a small bastion, which has now disappeared. The walls are in disrepair in some places and it is likely that some more restoration work will be carried out soon.
Saint-Omer has a fairly major station, with frequent trains from Calais and Lille. It is also accessible by motorway (the A26 from Calais or the N42 from Boulogne). Other than the remains of the fortifications, which are in a park adjacent to the Boulevard Vauban, there are two important religious monuments and two nazi military installations in the area. The 800-year-old Notre Dame Cathedral is situated just behind the surviving stretch of ramparts and the ruins of the Abbey Saint-Bertin are on the other side of town nearer the station. Near Watten (to the north of Saint-Omer) is the Blockhaus d'Eperleques, a massive conrete construction built by the nazis for assembling and launching V1 rocket bombs. Following allied bombing raids, a new base, known as La Coupole was then built near Wizernes (to the south of Saint-Omer).
This base would have been capable of launching deadly V2 rockets against London, against which there could be no defence. The allies captured the bases before they could be used, but both are reasonably intact and can be visited today.