In 1546 the Spanish built a new fortress called Mariembourg to defend the southern frontier of the Netherlands. In 1554 the French captured Mariembourg, so the Spanish built the fortresses of Philippeville and Charlemont (Givet) to the north. In 1659 the Treaty of the Pyrenees'gave Philippeville to France. This left a dangerous gap in the frontier defences between Mons and Namur.
As a result the Marqués de Castel Rodrigo, the governor of the Spanish Netherlands, ordered the construction of a new fortress on the river Sambre. The site chosen was the village of Charnoy, on a hill on the north bank of the river, protected on the east and west by small streams.
The ground sloped gently upwards to the north, but the hill dominated the ground to the east, west and south (towards France). The new fortress was called Charleroi in honour of Charles II of Spain, a slight change in name from Charnoy.
The new fortress, designed by the Flemish engineer Salomon van Es, was hexagonal with six bastions. There was a dry ditch'and probably several outworks around the fortress. Construction started in 1666, but was not very far advanced when the French invaded the following year.
The Spanish mined the incomplete ramparts and retreated, leaving Turenne'to capture Charleroi. The French occupation of Charleroi was confirmed at the Treaty of Aix-la-Chapelle'in 1668. Soon afterwards, the French began to rebuild the fortifications.
Under Vauban's'the slighted Spanish fortress was rebuilt to the same plan with additional outworks and a hornwork'facing south-west. The two streams were dammed to form inundations'protecting the fortress. Privileges were granted to encourage people to move to the new town.
In 1672 it was decided to build a bridge over the Sambre so that reinforcements could easily reach the fortress from France (to the south). This led to the establishment of a lower town, the Ville Basse on the south bank of the river.
The ground between the river and the upper town (Ville Haute) was protected on the west and the east by two demi-bastions'and a demi-lune. When these works were finished, Charleroi was a formidable fortress, but the French had to give it up by treaty'in 1678.
After more than a decade in Spanish hands, Charleroi was attacked by the French during the Nine Years' War. In the siege of 1693 Vauban found himself attacking the defences he himself had designed.
Vauban attacked the upper town from the high ground to the north of the fortress, taking one of the outlying lunettes, whilst a secondary attack aimed for the western dam. He then had trenches dug along the reverse slope on the west side of the upper town.
This reverse slope enabled the French works to be completely hidden in dead ground because the slope was too steep to be overlooked from the walls.
The French batteries quickly battered a breach in the walls and the Spanish garrison was forced to surrender. Following the siege, Vauban constructed a series of tiered works running down the slope between the upper town and the western inundation (see right).
These new works were designed to stop an attacker from exploiting the weakness that Vauban used in his attack. In 1697 the Treaty of Ryswick'returned Charleroi to the Spanish.
Charleroi was given to Austria along with the rest of the Spanish Netherlands in 1715. The town was at peace until 1746, when the French laid siege to it again. The French troops gained entry to fortress when pursuing the fleeing garrison of one of the outworks that had just been taken.
During the French occupation the fortifications of the lower town were demolished, but the upper town was left intact. Charleroi was returned to the Austrians in 1748. The remaining fortifications were partially dismantled in the 1780s, only to be hastily reconstructed in 1792 as Revolutionary France grew powerful.
The French captured Charleroi in 1794 after bombarding the town and its fortifications. After the Napoleonic Wars the Austrian Netherlands were given to the Dutch, who decided to rebuild the fortress of Charleroi to protect the Netherlands against French attack. The new fortifications were planned by a Dutch engineer called Oortwijn.
Oortwijn's design roughly followed the old fortress, although the upper town was extended to the north to take advantage of the high ground there.
However, the new fortress did not last long in this state. In 1829 the Sambre was canalised the fortifications of the lower town were demolished to make way for new industry using the river. The upper town, however, remained fortified and garrisoned.
In 1830 Charleroi fell to the Belgian revolutionaries, becoming a Belgian fortress instead of a Dutch one. Eventually the pressure of industrial growth in Charleroi and developments in artillery led to the demolition of the fortifications of the upper town between 1867 and 1871.
Today there are very few reminders that Charleroi was once a fortress. The industrial growth in the late 19th and early 20th centuries encouraged the construction of new buildings. Not only are the fortifications gone, but very few buildings have survived from the fortress era.
The street plan of the upper town around the Place Charles II can still be seen today, and there are a few remains of Charleroi's fortified past dotted about the city.
There is a retaining wall and vaults underneath Rue de Montigny (which can be seen in the Parking de l'Innovation and the café Le Corto) dating from the French fortress. Some of the countermine galleries of the Dutch fortress survive and can be visited by guided tour.
Apart from this there is little to see in Charleroi, which is a rather run-down post-industrial city. There is a main line station (called Charleroi-Sud) which is served by regular trains to Brussels, Lille and Liège.