The allied Pragmatic Army's attempt to relieve the siege resulted in the decisive French victory at the Battle of Fontenoy on 11 May.

[1] The city, whose population then amounted to 21,400 inhabitants, was part of the Barrier Forts, established since 1714 by the Dutch Republic as a defensive line against France.

Van Dorth immediately had Tournai's suburbs set on fire and ordered a sortie on Orcq, which was easily repelled by the French cannon.

After a series of diversionary moves, Saxe laid siege to Tournai on 28 April with his main force of 72,000 soldiers.

[3] He moved his men into the siege lines, crossing to the left bank of the Scheldt in order to surround the Vauban-designed citadel.

French engineers constructed pontoon bridges at Calonne and Constantin to enable communication and movement between Saxe's forces on both banks of the river.

That afternoon, an accidental explosion in the French lines caused the death of the Marquis de Talleyrand-Périgord and the siege engineer, Desmazis.

[6] On 11 May, during the battle of Fontenoy, a small number of Dutch cavalry from the garrison attempted a sortie, which was repulsed by the French besiegers.

With the Allied defeat at the Fontenoy, Saxe successfully removed the threat of the British and Dutch relieving the siege.