When the Neufosse Canal was cut in the 1820s to link the Aa to the Lys, engineers had to solve a problem: the land rose more than thirteen meters between Saint-Omer and Aire-sur-la-Lys, and a staircase of five conventional locks at Fontinettes was so slow that barges waited a full day to pass. In 1888, the French built a hydraulic boat lift - effectively a giant elevator for boats. A barge floated into a steel caisson full of water; the caisson was lifted on a single hydraulic ram counterbalanced by another caisson descending. In three minutes a boat climbed thirteen meters. It was a marvel of Belle Epoque engineering, similar in principle to the surviving lifts on the Canal du Centre in Belgium. The Fontinettes lift operated until 1967, when a new lock replaced it. The lift itself remains, preserved as a monument, its caisson empty and its great iron gears still.

If you have eaten in a French restaurant, you have probably drunk from Arques. Arc International - originally Verrerie Cristallerie d'Arques - was founded in 1825 and turned the town into one of Europe's great industrial centres. At its mid-twentieth-century peak the company employed more than ten thousand people, melting silica and soda ash into the Luminarc and Cristal d'Arques lines shipped across the world. The town's center even features a glass-themed roundabout, and a brewery, La Goudale, has relocated here from Douai to brew alongside the glass furnaces. Arques is a working town where one industry sets the rhythm - shift changes, ovens running through the night, the orange glow of molten glass visible from kilometers away when the wind tilts the steam plume the right way.

In April 1303, in the angry aftermath of the Battle of the Golden Spurs - when Flemish weavers had butchered the flower of French chivalry at Courtrai - another battle was fought here. The Flemish won again, briefly. Then, in July 1340, the English commander Robert III of Artois razed Arques to the ground on his way to besiege Saint-Omer. The town was rebuilt. Two hundred and ninety-eight years later, in 1638, the French would capture Arques as the first move in a Thirty Years' War siege of Saint-Omer they would ultimately lose. The town sat on the wrong corner of every northern war for five centuries. The lift and the glassworks tell only the calmest layer of its history; under that is medieval blood, and under that, possibly, a Roman harbour that vanished when sea levels dropped.

North-east of the town, the Audomarois marshes spread out across the flatlands of French Flanders - a maze of canals, drainage ditches, and floating market gardens that has been worked since the Middle Ages. The Parc Naturel Regional des Caps et Marais d'Opale stretches from these wetlands all the way to the Channel cliffs. Arques sits at the junction of two worlds: industrial canal, with the lift; rural canal, with the cabbage farmers of the marsh, who until very recently still poled flat-bottomed boats called bacoves through the reeds to bring their produce to market in Saint-Omer. The town is a ville fleurie rated with three flowers, and there is a town walk - the Circuit du Pave - that ties the lift, the chateau, the church, and the canal locks into a single afternoon.