The town of Tournai stands on the river Escaut (Scheldt) in the province of Hainaut. It was fortified in Roman times and later became the capital of the Frankish Kingdom, remaining part of France when the Frankish kingdom was split. The town had a significant textile industry and grew in importance in the middle ages. The Roman walls were repaired in the 10th century in the face of Norman attacks, but they were too small to protect the growing town. In the 12th century a new set of walls was built to protect Tournai. A second, large set of walls was built in the 13th century, which included two arched water gates where the circuit crossed the river.
In 1513, an English army under King Henry VIII attacked Tournai. The garrison was poorly equipped and the fortifications were not ready to face the English guns, so the town fell after only a few days. The English recognised that there were anti-English feelings amongst the population and they needed to put Tournai in a better state of defence. This work entailed the construction of a citadel to house the large garrison. This was achieved by building two internal walls to enclose an area within the defences in the north-west corner of the town. These improvements included the first artillery fortifications at Tournai: round towers with thick stone walls, an earthwork bulwark and some "boulevards" (outworks). The English occupied Tournai until 1519, when the town was given back to France.
In 1521 Tournai was captured by Imperial forces and annexed to the Spanish Netherlands. The French garrison held the town for 6 weeks and then retreated into the citadel before surrendering 2 weeks later. This long siege suggests that the English works, although primitive by later standards, had improved the strength of the fortress. From 1527 the Spanish began to reinforce the defences of Tournai. Demi-lunes were built in front of the walls around the town. The medieval walls were backed with earth and artillery was mounted on them. During the 80 Years War Tournai rebelled against Spanish authority and held out for 2 months against Spanish forces before capitulating. After the siege many of the Protestant leading citizens went into exile and the town began an economic decline.
After over a century in Spanish hands, the French returned to Tournai in 1667 under King Louis XIV. The siege was conducted by Vauban, the king's engineer, who reduced the poorly-garrisoned fortress in just a few days. Soon after the French capture, Vauban was busy drawing up plans to improve the fortifications. Not content with the numerous Spanish demi-lunes outside the medieval walls, he drew up plans to construct even more outworks. Some of the smaller works were reinforced by outer ravelins, four large hornworks were built and various outlying redoubts thrown up. However, the major improvement to the fortifications of Tournai was the construction of a massive pentagonal citadel. This citadel, which was designed by the engineer Mesgrigny (under Vauban's supervision), was situated on the high ground at the south-east corner of the town. 300 houses had to be demolished in order to make room for its construction. The citadel had five bastions and a central courtyard, similar to those at Lille and Arras. However, it differed from these in several areas. Firstly, there was a continuous false bray, or lower wall, in front of the main wall, giving the defences an extra tier of firepower. Secondly, both faces of each demi-lune were defended by a strong bonnet (a triangular work that sits alongside another outwork). Finally, there was an extensive system of countermines around the citadel. The approaches to the town could be flooded using the river, but the citadel stood on higher ground, so it could not be protected in this manner. To offset this disadvantage, the countermines enabled the garrison to lay mines beneath an attacker's positions and blow them up. With this new citadel, the old English garrison area was superfluous, so its internal walls were demolished during this time. Most of the work on the new fortress was complete by 1688.
The new French fortress saw action twenty years later during the War of the Spanish Succession. In 1709 the Allies laid siege to Tournai. After three weeks the garrison surrendered he town and retreated into the citadel. For seven weeks they held out against the besiegers, causing havoc with the countermines under the Allied trenches. Eventually the attackers reached the ditch and battered a breach in the citadel's walls, bringing an end to the costly siege. The fortress Tournai had proved its worth to France.
The Treaty of Utrecht, signed in 1713, passed Tournai back to the Netherlands (now the Austrian Netherlands), although a Dutch garrison was placed in the town. In this period the hornworks were abandoned, but some of the demi-lunes were strengthened with casemates. The French briefly recaptured Tournai during the War of the Austrian Succession in 1745, returning it in 1748. In 1781 there was a proposal to demolish the fortifications, but this was suspended when the French Revolutionary Wars broke out. The fortifications were finally dismantled in 1863.
Today, little remains of the once-impressive fortress of Tournai. However, remnants of all the various eras of fortification can still be found scattered across the city. The Tour du Cygne and the Fort Rouge, towers from the first medieval circuit, are both in good condition. The Pont des Trous, the western arched gate over the river from the second circuit, can also be seen. The central arch was destroyed in the Second World War, but it has been restored to something of its former glory. Another stretch of walls from the second circuit can be seen on the east side of the town leading north from the river.
A large circular tower built during the English occupation, known as the Tour Henry VIII, also survives. It is 25 metres in diameter and the walls are 6 metres thick. However, there are virtually no remains of the vast work undertaken during the French period. The citadel has been demolished, although there are some remnants to be seen. The Porte Royale, the gate facing the town, still exists as well as some masonry fragments and casemates nearby. The countermines of the citadel were buried when the fortifications were demolished, but they still exist and it is sometimes possible to have a guided tour of some of the tunnels. Tournai is easily accessible by rail and road, being close to Lille and Courtrai, on the border between France and Belgium.